As a lot of people pointed out, not a lot of people have impressive sound systems. I'm the only person I know with a 7.1 setup. My parents have a 5.1 setup, but the video games aren't plugged into it. My uncle has a 5.1 system, but the 2 rear speakers aren't even in remotely the right area and he hasn't used it in years. They just use the TV speakers. Other than that I don't know anyone with a surround system. Also, most the surround systems I've seen posted on this website are the junky HTIB systems that you can pick up for a few hundred dollars. So, while the PS3 can handle 7.1 (which is part of the reason why I bought a 7.1 setup along with movies) advertising it will be of little benefit.
As for advertising blu-ray, everyone knows what it is now (thanks to advertising) and HDTV's are the popular thing to buy now (a lot more than decent surround systems) so a blu-ray player is the perfect addition. Why not advertise that this unit will be able to take advantage of that new expensive TV you just bought?