As a former bicycle mechanic, and as someone who spent a lot of time on a bicycle during my high school and college years, I would even go one step further and say that bicycles need a lot more service, mile per mile, than your average car. One way to think about this is to think about how a typical bicycle would hold up to the rigors of a 30 mile daily commute, 5 days a week, 52 weeks a year. This would add up to about 7,500 miles of riding a year, which is on the low side of what the average car in the United States is driven. A good bicycle is engineered to minimize rolling resistance due to the fact that its human powered powerplant can only sustain an output of about 1/4 horsepower for a decent length of time, champion athletes a bit more, couch potatoes much less. The average automobile/passenger package has about 15 times more weight than a bicycle/rider package, but typically has at least 500 times more horsepower to work with, assuming a 200 pound bicycle and rider with 1/4 horsepower, and a 3,000 pound car with about 150 horsepower. Let's take a look at what the typical life and maintenance requirements of various components would be:
Tires: On a typical car, tires have about 3/8 inch of tread on them when new, and usually last 50,000 miles or more. Their steel belts and thick tread also resist puncturing by bits of glass, small bits of metal, thorns, and other road hazards. This robustness comes at the cost of much higher rolling resistance than a bicycle tire, whose thin narrow treads can be easily punctured, and the entire tread scrubbed off in one place during a panic stop. In my experience, even high quality bicycle tires carefully ridden will last no more than 5 thousand miles, and will likely have at least one puncture during that time.
Wheels: A typical automobile wheel is either a heavy steel pressing or of cast aluminum on better vehicles, and weighs about 20 pounds or so. If you include the brake rotor, spindle assembly, and hub, this will bring the whole mess to about 75 pounds. A good bicycle has aluminum alloy rims made of very thin metal buttressed by spokes stretched at great tension to give the wheel rigidity, and also serves as a braking surface. The entire front wheel weighs less than 3 pounds on a good bike, the back about 5, including the freewheel. Since the rim is also the braking surface, any radial or lateral runout that occurs as a result of uneven stretching of the spokes or damage to the rim compromises braking ability and/or causes the brakes to drag, and must be dealt with. Hard riding, rough roads, or a heavy rider can make wheel truing a weekly ritual to keep the bike in top shape.
Chains and Cogs versus the Automotive Transmission: Automotive transmissions typically will last 150,000 miles or more, even without their recommended fluid change every 36,000 to 60,000 miles. Their moving parts are made of hardened steel and are enclosed in a clean and sealed system where they are bathed constantly in clean oil. A bicycle, and many motorcycles as well used exposed chains and cogs. An ordinary motorcycle chain typically has a maximum life of about 10,000 miles, the newer O-ring chains about 20,000 miles, provided it is cleaned and oiled every few hundred miles. Bicycle chains, particularly on the newer 18 and 21 speed models are built even lighter and more flexible than motorcycle and even chains for bikes with coaster brake and 3 speed hub systems. derailleur chains are also literally dragged from one sprocket to another, and will start jumping cogs after only a couple of thousand miles. The cogs themselves will wear out too, especially if the chain is not kept clean and oiled, or allowed to rust. Derailleurs can destroy themselves instantly if misadjusted, and constantly need minor tweaking due to wear and cable stretch.
Bearings: Bearings on most better modern bicycles are mostly sealed types today, with the exception of the steering head and bottom bracket, which are vulnerable especially if the bike is left out in the rain. Non-sealed bearings need to be serviced at least once a year, more often if they see heavy use, or are exposed to water, dust or mud.
Brakes: Automotive brakes use friction pads that start out about 1/2 inch thick, and are about 10 square inches in size. They use a material that is a bakelite/semi-metallic or asbestos composite that is only slightly softer than the cast iron rotor or drum they press against. They are actuated by heavily built hydraulic cylinders which weigh in at about 5-10 pounds each. A bicycle brake has about 1/8" to 1/4" of usable pad, which is only about 1/2 square inch in area at the most. The pad material must also be soft enough not to gouge the thin and soft metal of the aluminum alloy rims. A caliper brake or a cantilever brake weighs only a few ounces. While stopping a 200 pound bicycle and rider from 15 miles an hour is a far cry from stopping a 3,000 pound car going 80, the bicycle's brakes are built as light as possible to save weight. Because the material for the pads must be relatively soft, they usually need replacement every few thousand miles. Cables need to be adjusted after a period of stretching in, and as the pads wear down. Even taxicabs in urban areas can usually get at least 20,000 miles from a set of brakes, while expressway cruisers can often go 80,000 miles or more. Hydraulic automotive brakes also have the virtue of being self-adjusting.
Recommendations: The typical modern high performance bicycle will carry its rider as efficently per unit of energy spent as just about any other machine yet devised by man, but it comes at a great tradeoff in robustness compared to the typical Toyota Camry or Honda Accord seen crowding the highways. If you are considering commuting by bicycle, be aware that unless you are at least somewhat mechanically inclined, it means that you will be spending a lot of time and money shuttling the bike to the shop for maintenance and repairs. If the terrain is fairly flat where you commute, you may be able to save on some of the headaches by riding a good quality, but single speed bike with an internal hub brake. Good bikes like this are hard to find in the States, but a reasonable compromise might be a light-duty mountain bike or a hybrid bike, which tend to be much more robustly built than a road bike, though sadly not nearly as responsive. Another recommendation when selecting or building a bicycle for commuting is to avoid not only the low-end department store type bikes, but also the very high end types of bikes and components they are built from. The very high end stuff is often made from exotic materials such as carbon fiber or titanium and is outrageously expensive, and the main benefit is a very small incremental savings in weight for most things. This is especially true for wheels and tires for road bikes. The very high end stuff will be light as a feather and be a joy to ride, but especially ultralight wheels tend to buckle under the first serious pothole they encounter. Ultralight tires will roll with almost no resistance, but will puncture on even the slightest hazard, and have little or no spare rubber for those panic stops.
Learning to do your own repair and maintenance on a bicycle is not very difficult, it mostly takes common sense, a good eye, a general bicycle repair manual, and a few simple tools to do most common repairs. It is not nearly the hassle as servicing most cars is today.