You could make the case that a laptop is portable computer with its most important input and output devices built in. You could make the case that the laptop computer is a miracle of engineering that allows complicated tasks to be done on the go. If you were to make such a statement, you would be making a statement for about 1 to 10 percent of the people who own, use, or want a laptop.
For the other 90 to 99 percent of people interested in laptops, the interest seems to be based on two things. One is obvious, the fact that laptops are expensive items, and make good status symbols. Not only are laptops a good example of conspicuous consumption, but they also show that the bearer is not only consuming, but is probably producing, doing such culturally and economic important tasks as writing the Great American novel, keeping updated on the blogosphere, and hacking into the aliens central control computers by typing in "override security". Someone with a laptop is obviously an important person, who can not let a little trip to a Starbucks distract them from keeping in touch and on top of things.
Along with this, and perhaps not appreciated as much, is the fact that laptops tend to bring out people's raccoon nature. I have seen too many people get a scary little glint in their eyes when confronted with a small, gleamy metal object, even when they had no idea why or what the object was for. Even when people can't invent a function they need their laptop for, the siren song of something small, metal, with hinges is beyond most people's control.
However, I realize that there are people who may need a certain tool. Maybe you actually are rappelling down into volcanos to do research on lava domes, and need to send wi-fi notes to the field office. But before you think about getting a laptop, there are a number of things to consider. To understand this, you have to first understand a number of things about desktop computers. Despite the different brandnames, all Intel architecture computers for the past 20 years have used interchangable parts. Most of those parts are of course, obsolete, but some are not. For example, the power cable from a 80286 computer would still fit the newest Pentium-IV desktop system. Laptops, on the other hand, use a great deal of proprietary parts. Since laptop models change every few years, and there are several major manufacturers, what happens when the power supply, battery, screen, CD Drive, etcetera go bad on your 3 or 5 year old laptop? This is not a rhetorical question, since I hardly have an answer myself. Apart from the fact that the parts are going to be expensive (which of course, is not an issue for the type of serious career professional who needs a laptop to catch up on business in the local coffee shop), they are going to be rare, perhaps no longer made, and finding the neccesary part may involve a very long search. Especially when you know that you need a "Dell power supply", the concept of volts and amps being left for the little people who need to know such technical trifles.
So, to sum up the laptop question:
A. Are you an engineer, working in the field, perhaps rappeling down volcanos or tracking tornados?
B. Will you pay hundreds and thousands of dollars for something because it shiny, and hope that it doesn't get ruined when you run it through the water before eating it?
If yes, go to question 2.
If no, get a real computer.
2. Do you have the money and time to do serious research and hunting for the neccesary hard to find, expensive part when your laptop dies? Will you spend the grueling hours needed to learn technical terms like "volt" and "amp" when your power supply gets coffee spilled on it and needs to be replaced?
If the answer to this question is yes, then you do, indeed, need a laptop, and also, please message me, I have some swampland in Florida to sell you.