The problem which I see with comments on both sides of this thread is the assumption that one can hoard money, or that money can be put somewhere where it "just sits." The problem is that, unless Mr. Gates, et al. are taking CASH (paper) and making stacks of it in their basement/attic/wherever the money isn't just sitting anywhere.
Even if they just put it in a bank account (which is about the closest to making a pile out of it) it is then circulated through the economy via increased ability for the banks to loan, etc. (Ok, I am oversimplifying, but the point is still accurate.) More likely is that thier money has been invested somewhere. The reason that the rich can make more money in investments than the comparitively less-well-off is that you have to have a certain amount of money to be legally allowed to invest in the riskier investments, which are the ones which pay off big (or fail big). That risk of big failure is restricted to the rich exactly because they are less likely to be "hurt" by a failure, so if they get conned, they can afford it.
In any case, their accumulation of cash is still working in the economy, providing start-up loans to new businesses so that people can be hired, etc.
As to the non- or anti- productive examples given by the parent post: Just because sometimes a business has to downsize to better match the current economy, doesn't mean anything nefarious is happening. If you are making more product than you can sell, then you are making too much product. A stock buyback does affect the stock price, but it is essentially just the company becomming owned by fewer people, the people who sell the stock back have been compensated for their prior ownership, and are free to buy something else with their money. There may be a point to questioning the bubble speculation, but to fix that would be to further disallow smaller investors and only allow the richer investors to risk the bubble. Even in that case, every new industry may just be a bubble, and is a gamble, until it proves that it isn't. If you outlaw risk (overstated), then you will never have anything new (also overstated, but you get the point. I hope.).