JL, what you addressed isn't really the crux of my comment but I'll respond.
I'm not arguing that Sony doesn't need the PS4 to sell well to recuperate their R&D expenses. I'm saying that Sony will continue to target two separate price markets with the PS3 and PS4 as will Microsoft with the 360 and X1. Gaming consoles are a fairly elastic good. As long as there is a demand for the older, cheaper, consoles and software from a segment more sensitive to price, it makes no sense not to continue selling that product line. These consumers are not likely to buy the newer, more expensive, console just because a cheaper console is no longer available. In general, this strategy isn't much different than the strategy any other technology manufacturing firm uses (e.g. Apple, Samsung, etc.)