Because the company needs to get the kinks out of the games & get feedback on the product.
People have been shot over these things. Why hype the h--- out of it then, if it is just a trial balloon? Do they not test these things before they market them? (Of course,the companies do not really have to hype them, the gamer magazines and websites will do that for them.) Although, I do understand that there is no better test and source of feedback than the millions of kid s who live and breathe for these devices, which is of course reltively better than being out shooting and robbing people.
Game consoles are sold at cost and the manufacturer makes their profit on the sale of games, which have a large profit margin. The reason Sony limited the production of consoles is to manage their cash flow, they don't make any money on them. Soon some Linux hackers will install Linux on these consoles because it's a cheap way to buy a high powered computer for a fraction of the cost of a similar PC.