Think about that. I don't know about PSone, but with early PS2 years and with PS3 Sony had losses. Huge ones according to some. Current situation of the PS3 might be better with the slim model, but before that Sony was in the black. Pitch dark black.
Would Sony be a better, more competent and profitable company if it's gaming division was focused only on game development for thirds?
I cannot see a Sony IP failing if properly implemented honestly. Games like Gran Turismo, Uncharted and Killzone would sell amazingly well on a console as the 360, while Ape Escape and Jak and Daxter would be the best games on a console like the Wii.
Sure they would also sell on their own hardware (and sells)... but the losses on hardware minimize such profit.
Sony as a company, stock holders, both Nintendo and Microsoft, gamers... Wouldn't it be better to everyone?