If they buy stocks, yes, they put up capital to build factories - but factories don't create demand. Pay wages before profits start coming in? perhaps they do not, that is what investors (or the rich if you wish) come in, and they are paid very handsomely for that, if it is sucessful. The point remains, sure, there are contributing factors but demand is what runs this country. Reducing taxes for the rich does not create demand (well, a little bit I will grant you, but not enough to perpetuate an American Economy).
Without workers, the factories don't run, without consumers the factories don't turn a profit. Simple as that. The rich don't want us to realize that we are the ones who create the wealth, they want us to think they do. They want us to think that somehow THEY create demand for products and services and somehow if we give them larger and larger tax breaks the economy gets larger and larger - we see in princple and in practice that this is bullshit.