They certainly could, but it is the *promise* and *hope* of these riches that fuels much of the activity of the lower stratas. The American Dream is all about hard work leading to wealth and comfort.
Now, we could debate whether or not the American Dream is still a reality, but most people still believe in it. Yes, many at the bottom realize they'll never get there themselves, but hope that they can give their children a chance to make it...through education and opportunity.
If you force the rich to subsidize the poor, you take away the incentives of the poor to become rich *and* the rich start trying to find ways to avoid paying...which they will because they can afford to hire people who can find ways around almost any law.
IMO, communism will always fail on a large scale because people have little inner passion to excel. Without outside pressures, communistic states will inevitably stagnate due to this lack of passion on the individual level. It happened in the Soviet Union and it may happen in China. However, China does have some non-communistic pressures which may offset or delay their stagnation for a time. But if they cannot overcome some of those pressures, such as population, they are just as doomed as the Soviet Union.
That's my opinion on the matter.
Tuor