The Gran Turismo series has always been the most real to me. By that I don't mean the graphics, physics, or such, but the attention to detail these guys are willing to go through with their car modeling. I mean, for 60% to be the priority for car modeling is huge, very huge. Granted, there are other simulators out there that may very well "seem" to care as much, but knowing Kaz and his passion for cars and racing, it's like an unbelievable chemistry.
Somehow, I feel the connection between Kaz and his games. It shows by how his games would include every aspect of automobile racing like motorbikes, rally, F1, road, GT and now drifting. He even honors the old classic cars by including the likes of the useless carriages in GT4, and concepts that had not been or soon to be in production. Also, how they would include hundreds of cars must mean something. GT2 had over 500! and I don't think any other developers out there would go through that for a racing game as early as the ps1 days.
The thing is, the first Gran Turismo opened up a whole new world. No other games before would even attempt to recreate realistic driving physics, let alone in a system as limited as the PS1. This includes their trademark for including a huge amount of cars. They've set the bar and I know Kaz is not just going to drop it and let others take that away. It'll be like Sony giving up to the Insignia company.
I guess in conclusion it's just because I really feel the connection between the passion and how Kaz/PD incorporates that into the game. It's something I don't feel in other games, and this is a real, honest response from me.