LOL. Well it's hard to argue with flat out fanboyism, however judging from the "professional" reviews, not to mention thousands of posts in these forums, there is an objective consensus emerging about GT5:
the game has excellent physics, (for the most part) outstanding graphics & a nice track selection with some first rate "special effects", but the gameplay, design & functionality of the game are sub-par.
Even if you don't accept the latter part of that description, there's no denying that PD failed to deliver their benchmark graphics for most of the cars & some of the tracks featured in the game. I think we can agree that KY did not plan to deliver a game with most of the cars rendered in "Standard" graphics. My guess he just ran out of time - the quest to include 1000 cars fell short in the end & the resources spent on trying to model all those cars took time away from working on other aspects of the game.
It's clearly not possible to deliver everything - choices & priorities have to be established. There may be a good reason to include a Prius in a "car-collecting" game, but is anybody going to spend much time driving it (let alone racing it) if they do "collect" it? Is it worth spending limited resources creating a car that people are unlikely to drive for more than a few minutes at best?
If GT5 has demonstrated anything it's demonstrated the upper limit of what PD is able to achieve in more than 5 years of development time, which has to represent the maximum time it's possible to go without having the whole project collapse under the weight of cost & frustrated expectations on the part of the fan base. If enough people get turned off & decide to "play something else", there won't be a GT6 - or at least not a GT6 that has the same epic ambitions of past Gran Turismos.