The reason I believe Sony's exclusives can't sell as well as they should this gen.

[superchunk]

I think its more to do with saturation markets and no clear superiority.

Nintendo makes THE best platformer, brawler, kart race, zelda-type, party games, etc of games there are.

These games are considered the best of the bunch and therefore sell extremely well.

Sony's first party, while generally technically good games, are not the cream of the crop.

Killzone is about as good as Conduit... save for online play which is 100% Nintendo's fault and not the games.
Uncharted is no better than Assassin's Creed or Batman or many other adventure games.
GT is comparable, though maybe better slightly, to Forza or other simulation racers. (However this is the closest Sony has to a top of the class game)
God of War is no better than or worse than IMO AC/B/others.

Frankly, their titles just don't stand out in the crowd in almost every case. The only game I'd give props to, to being uniquely different and top class would be their platformer LBP. Its not the best platformer alive as that belongs to Mario, but the creativity it adds and virtually endless alterations of platforming, do make it a top tier game. But they do need to revolutionize it better in the next iteration.

In reality this thread and overall argument goes into the idea of why Sony cannot exist solely on its own software. I've made that comment multiple times and its easily proven by looking at the sales history of Sony's first party titles on any of its consoles. They are always dwarfed by 3rd parties in the same genre.

But, I'd also agree that marketing their big franchises in other mediums would significantly help. Sackboy, Drake, Kratos, etc... all have potential. Especially considering the content Sony owns in music and video. You'd think they would have already done this.