I'm not saying the studio's aren't good. I'm saying that I don't see how they're viewed as some incredible anomalies compared to the rest of the industry, in the way that many here portray them as.
I hardly hate GT, but as I mentioned before Forza outscored it all last gen effortlessly, yet people are nowhere near as quick to laud Turn 10 in the way the way they do Polyphony Digital. They're a great studio, but they no longer stand alone, and haven't for years. Sure GT massively outsells Forza... but I'm guessing you won't apply that same logic when it comes to something like MotorStorm.
As for 343i and Guerilla Games. It's not really fair to claim that they've done nothing to move the series forward considering the team houses some prominent members of the original team. Killzone has never been on Halo's level regardless of if we're talking about 343i or Bungie, and 343i would have to do much worse than Halo 4 in order to draw any real comparisons to Shadowfall. If 343i actually gets to Guerilla's level, then I am fucking done with them tbh...
Every publisher has studios pumping out great games. For every God of War, there's a Bayonetta, Ninja Gaiden (sans 3), or Devil May Cry. For every Infamous, there's a Crackdown, Saints Row or potentially Sunset Overdrive. For every Sly Cooper, there's... well... a shitload of games to be quite honest. For every Motorstorm, there's a Project Gotham Racing 4, Blur, Forza Horizon, Burnout Paradise etc. These games don't tower over all their competition in the way that Nintendo games tend to, or Naughty Dog can be credited to, or Bungie did with Halo. They're simply good games, from good studios. Nothing more special than what many other publishers offer imo. Naughty Dog and Media Molecule are pretty much the only ones this claim can be applied to... and as we've established, MM only appears to have a single competitor who's first game is nowhere near complete.
It's really really easy to create shortlists of great games a publisher puts out. Sega, a supposedly awful publisher had Valkyria Chronicles, Yakuza 4, Bayonetta, Binary Domain, Total War 2, Sonic Generations, All Stars Racing Transformed and more last gen. EA had Mass Effect, Battlefield BC2, Crysis, Dead Space, Dragon Age Origins, Burnout Paradise, Mirror's Edge, Skate and more last gen. Microsoft had Forza Horizon, Alan Wake, B&K: Nuts and Bolts, Lost Odyssey, Viva Piñata: Trouble in Paradise, Crackdown, Project Gotham 4, Forza Motorsport 4, Gears of War, Halo 3 and more last gen. Konami had Metal Gear Solid and... well... anyway you get the point. Pretty much everyone is putting out good shit. The difference with some studios is that basically nobody is able to compete with them in their chosen field. This would apply to quite a bit of Nintendo's teams, and almost none of anybody else's. Sony included.