The roster of PS All Stars shows off Sony's greatest strength and weakness. On the one hand, Sony has constantly invested in new IPs. Smash Brothers features very few characters from the GC era (Olimar, Lucario sort of, is that it?), whereas Sony has a pretty nice variety of franchises they've created over the years. Parappa and Spike from PS1 (and Daniel I think. Dunno much about him really), Ratchet, Kratos, and Sly from the PS2, and Cole, Princess, Cole, and Sackboy from PS3 etc. They've constantly been developing new IPs, and it shows in the roster.
On the minus side, Sony hasn't been really able to create the same kind of sustained franchises as Nintendo has. While characters like Mario, Link, Samus, and Kirby have been relevant for 25 years or so, Sony's characters tend to have shorter lifespans. Nariko seems like a one-off character, Parappa has been forgotten by all but the most diehard fans, and Daniel and Spike are pretty obscure by this point.
Basically, Sony likes a constant rotation of fresh faces where Nintendo prefers to build on their past successes, which is why you see what you do in the rosters. In a few short weeks, we'll see which strategy was better.
