Regardless of Jim's comment or not, though there are no real evidence as to how many percent of gamers use BC on a console. I believe it is very much below 10% of the install base. It is much more the anticipation and expectation on peoples mind, that they would love the idea of playing BC games. But when it comes to it, I don't think many people actually would play older PS games. Below 10% I estimate.
It is much more a marketing deal to have BC in the portfolio of console specs, and the perception for consumers to have the option of playing BC games, rather than any other commercial incentives.