The reason why Sony is making so many new IPs is because at the time the PS3 came around they had few IPs of note, and none of the ones they did have were as bankable as Mario is. Let alone Zelda and Pokemon.
The big difference between Nintendo IPs and Sony IPs is that Nintendo IPs have been A LOT more successful, and have been around for a lot longer. Sony was able to rely on third party exclusives all the way until the PS3. With the PS3, pretty much ll of their big exclusives went multiplatform, meaning Sony had to develop new IP to fill the void. They've also had to team up with other developers to make exclusives like Heavy Rain and B3yond. Exclusive, I'd like to remind everyone, they do not own. Both trademarks are owned by the developer.
Sony is already experimenting with expanding their most successful IPs. LittleBigPlanet just got it's first spin off this year, just months after a platformer for the Vita. Uncharted just got it's first handheld release, just a month after the release of Uncharted 3 (or three months in America). And we can expect this reliance on successful, exclusive IP to continue to grow, because no company, not even Sony, wants to rely too heavily on untested, unproven IP. Once Sony has a substantial number of successful IPs under their belt (a threshold I'd say they've about met now), you can expect them to focus far more on those IPs then original titles, just as Nintendo and Microsoft currently do.
Frankly, I find this whining over new IPs to be silly. A game isn't made any better by having a new character. Super Mario Galaxy would not have been magically transformed into a better game if the Mario trademarks were removed. It just would have sold a lot less. The only thing that's really important is the QUALITY of the game.
And, well, Mario does have some of the most highest rated games of all time, so...
Of course, you can also expect them to continue to work on new IPs, just as Nintendo and Microsoft also have:
Day of Disaster
Dillon's Rolling Western
The Last Story
The Art Style series
All released in about the last six years. There are more, but I think this list gets it across well enough.