Here are ten reasons I can come up with, as a poor person in a rich country. They overlap a bit, but hopefully they'll answer the question.

The rich can find out

Your average refugee in the Congo does not have access to the Internet. They'll be lucky if they can find a copy of The Economist or The Wall Street Journal, much less Time or People or The Daily Mail. More than likely, they don't have access to CNN or Sky News on anything approaching a regular basis. They might be able to listen to the BBC World Service, if they know someone with a shortwave radio and if they speak one of the languages being broadcasted, but that's not going to help them too much.

Your average villager in India does not have an MBA and wouldn't be able to afford the tuition at any college or university, even assuming that they had received enough primary education to be able to read the textbooks. They will not know what a stop order or an IPO is, and they'll probably be lucky if they understand even the fundamentals of a stock exchange.

For the most part, poor people don't know what's going on, except in their immediate vicinity. They don't know how rich people make money, and they don't have the resources at their disposal to find out. This is as true of people in the ghettoes of America as it is true of Bedouins and Mongolian tribesmen.

The rich can invest
Making money requires an initial investment, no matter what kind of business you're engaged in. Lawyers have to pay for law school and/or a bar examination, their suits, their office. Shopkeepers have to rent a shop and purchase inventory before they sell anything. Televangelists have to pay for hair treatments and onion-laced handkerchiefs. So it goes. Unless you already have money, you can't get in.

Of course, you can work and save money, but this places poor people at a definite disadvantage to rich people, who can just pay for their stuff and get going. George W. Bush sure as hell couldn't have saved up enough to buy the Texas Rangers by working at Burger King.

The rich can travel
In most industries, making money requires a lot of time driving, flying, or boating to get from your supplier to your distribution point to your end user. Rich people can afford to transport their goods and services, and they can afford personal travel to sell their products. Poor people cannot... at least, not on anything approaching a regular basis.
The rich can diversify
Check out what Wal-Mart has done to mom and pop stores in cities and towns all across the United States. The little guys can eke out a decent existence until the big guys show up, offering more stuff in one place for less money. And then the little guys go with a splat.

Check out Microsoft for another example. Thanks to the success of Windows 95 and Microsoft Office, Internet Explorer was able to compete Netscape and other Web browsers out of the market. Whether you think that legally constitutes unfair competition or not, it certainly shows that having more stuff to throw at a market can give you the upper hand.

The rich can bribe
In autocratic countries with a mediocre semblance of law (like the United States), bribes go a long way. They can take many forms, too. A wealthy drug dealer can give a Mexican police chief a sumptuous mansion in exchange for letting the wares go through. Alternately, a big airline can consistently lure passengers back with free trips to places the little airlines can't serve. Alternately, a tobacco company (or ten) can pay for the election of a senator to block any laws that are proposed against them.

If marijuana growers could fund a senator, we'd probably have free dope in this country... but they don't, so we don't. So the rich tobacco growers get richer, but the poor cannabis growers get poorer.

The rich can muscle
Just look at War on Iraq 2003 and tell me this ain't true. If you can afford enough guns and bombs, nothing else matters except what you want. (This applies to Osama bin Laden, too... do you think that poorer terrorist leaders could have pulled off what he pulled off?)

If you want to see this in money-making action, check out what ITT did in Chile, or what Shell and Exxon do in South America and the Sudan (thanks to mkb for reminding me about the latter).

The rich can network
Partly because they can travel so easily, partly because they all speak English, and partly because they can afford to eat at the same expensive restaurants and vacation at the same expensive resorts, rich people interact across long distances and divides in a way that poor people cannot. If a good business opportunity pops up somewhere, the rich guys will be getting their friends in on it within hours, if not minutes. Poor people don't get cell phones or e-mail, so they miss out.
The rich can get credit
Most of the world's money is fabricated, and it's fabricated by and for rich people. A yak herder in Slavedominia can't have a public offering or put up collateral for a loan or sell junk bonds in yak manure, and they probably don't know too many people who supply venture capital. You can't buy and sell yaks on margin either, last I checked.

Likewise, a guy working on the loading dock at Wal-Mart is not going to be able to sell stock in his Geo Metro, even in the rare event that he can find a friendly enough banker to give him a 25% loan on it.

The rich can look good
This might sound frivolous, but it's not. Really poor people are usually dirty, smelly, and toothless. Most better-off people would rather give their money to someone who is clean and good-looking.

In addition, a woman with a good boob job and face lift is going to do better in most money-making fields than a woman who sags. That's just how life goes.

The rich can live
This, I think, is at the heart of the matter. If you're poor, you're too worried about survival to worry about getting richer. Paying for next month's rent and the family's groceries takes a much higher priority than long-term investing. Rich people, on the other hand, have disposable income and spare time way the hell above what they need to pay the mortgage on their penthouse and the payments on their Maserati, and they can easily divert this time and money to whatever project tickles their profit-making fancy.
Of course, if you believe in Heaven and Hell, this is all moot, since a lot of rich people are going to end up getting screwed in the butt by Satan anyway.