Since most rational points have been ignored I will reiterate ...
In order to see a noticeable increase in sales long term a system has to attract people to buy a system who were previously not interested in it. When a system's price is cut you typically see a massive spike in sales early on as people who were already going to buy the system rush out and buy it earlier than they normally would have; and when it is a price cut caused by a sale at a single location you also get a spike from people buying it from that retailer rather than from the store they would have bought it from before. The system selling fast does not mean that there has been any increased interest in the product.
To put it another way, I regularly browse a site where members post deals and bargains as they find them. Recently, there was a deal for a 500GB hard-drive for (around) $50 were 100 hard-drives sold out almost immediately. Now how many people think that if every retailer was regularly selling 500GB hard-drives for (around) $50 they would sell like crazy, and how many people think that everyone who were in the market for the best of the cheapest hard-drives was attracted to the sale?
Certainly, a $300 PS3 will sell better than the current $400 PS3, but in the long term it is unlikely that the price cut would do (much) more than return the PS3 to the level of sales it was seeing last year.
