I think to increase brand loyalty it helps. It's not absolutely necessary, but... if your console costs the most of all 3 (like the PS4 might), it would really help to increase the value I think, and to make people more comfortable with the investment (like me). I skipped PS3 because of the steep price, the lack of games I was interested in... I don't know if I will bother to get a PS3, but if someone told me the PS4 would be backwards compatible, I would be more inclined to get the PS4. Just because there are a handful of games on the PS3 I am interested in.
In short, I think it's a good gesture for a company to include backwards compatibility. It encourages people to play your older library who haven't and in turn, boosts loyalty in your brand and in the software you offer. For people who are already enthusiasts, it's not a big deal really except for convenience.







