I don't see any reason to think this generation, Sony's first-party efforts should be outperforming their previous efforts.
The PS3 user base is drastically different from that of the PS2.
Microsoft has taken away some of the (more or less) hardcore gamers, that's one thing.
But Nintendo has taken over practically the entire casual market, and it seems that they've been about half the PS2 user base (so there still are a couple dozen million people up for grabs out there - hence Project Natal).
Casuals are almost entirely avoiding the HD systems and go for the Wii. This is IMHO one of the big lessons of this generation, where no system has a monopoly of the market - that PS2 was covering very different segments in one piece of hardware. Cooking games, date simulators, social games, Harry Potter and Pixar games - all sharing their platform with the GTAs and MGSs and GOWs. Clearly there's been no overlap between their target audiences. But this time we have a quite sharp division between these segments, because Nintendo was able to grab the casuals before either of the HD systems was able to build up enough momentum (the Wiimote obviously helped a lot though). It also means that they aren't safe from a cheap Xbox3 or PS4's attack either.
The main consequence is that the hardcore AAA games should sell to a far, far larger percentage of the PS3 user base then on the PS2, or more similar to how they are selling on the Xbox360, because their target audience is concentrated on these consoles. Titles should not be compared to the relative performance of their PS2 predecessors, but to their absolute sales. If there were 10-15 million people paying for GT games, then these people should still be present and they most likely did not buy a Wii for driving games. Sales of the GT5 prologue show that many of them have already bought PS3s; lots of MGS fans are on board as well; and there's no GTA4 for the Wii either.
The other consequence is that without opening up to the casuals, both HD consoles' sales potential is very limited (no surprise here, though).
Do you think if U2 were exclusive to XB360 it'd have sold 6 million? I don't!
It should have sold at least 4-5 million units IMHO; but the point is that it's probably the best PS3 game and it's a disappointment that people don't like it. In this case expectations were high because of the quality of the game.
I think the games Sony produces just aren't the sorts of games that can sell above 10% of install base, with perhaps the fringe exception of GT.
Then Sony shouldn't concentrate their development efforts on those kinds of games, as exclusives should have wide appeal to sell the console and make a large return on their investment.
If their goal is to call attention to their console using these exclusive titles, then knowingly limiting their appeal defeats their very purpose.
I think your expectations are too high, and you're comparing successful titles to phenominal titles.
It was not my expectations, it's the expectations of the market, the press, the industry and the general internet using public too. KZ2 should have been a massive success after all the media and the hype and the money that Sony invested in it. Selling only 2 million units after all what's happened is a disappointment in every possible way, I'm just the one who says it out loud.
Same can be said about a lot of the other exclusives as well, only MGS4 has really managed to live up to its role so far.
Also note that some of Sony's exclusives have started their decline on the PS2 already so it isn't a trend just for the PS3. People either don't care about them, or they don't care about sequels, or they stopped playing games completely.
I think the games MS produces aren't the sorts of games that can sell above 10% of install base, with the exception of their shooters and Forza.
Viva Pinata, Banjo Kazooie, Lost Odyssey, Blue Dragon, etc. are all MS investments that haven't sold >10% of install base. That's because it's hard!
Again, games can sell to more then 10% of the install base today, because both HD consoles have a far more limited and concentrated user base then the PS2.
The reason for their moderate success is that they are inferior to the Sony exclusives and 3rd party titles in some way - quality, budget, branding, production values. MS produced them mostly to cover their bases, except maybe the JRPGs which I consider to be spectacular failures too. They've also almost entirely abandoned this activity by now.
But MS also made sure to cover the most popular genres to make money and sell systems with their efforts as well, so not all their exclusives are disappointments. Gears and Halo were all hyped quite a lot just as the Sony counterparts, there was a lot of scepticism as well - but they've all managed to deliver too. We'll see how Alan Wake fares, I have my doubts about that title; and I'm pretty interested in post-Halo Bungie games as well.
And it's also worth noting that multiplatform titles of all genres sell very well on both platforms. So it's not as much about the audience as about the actual titles IMHO.