LBP may be the one.
PS3 is doing pretty damn well for not having a defining title (outselling 360 over the same amount of time). It will be interesting to see what happens if it gets one.
On the other hand, I don't think Sony consoles generally have had them as much as others (Mario, Sonic, Halo). Sony has a huge number of compelling 1st party IPs, but none alone seem to define a system.







