In reply to the very first post... you can so finish gt2 100%, I have a save sitting here that proves it.  I think you have to have every single car, every race beaten, etc. 
*EDIT
And THPS is a very buggy series, especially the combo / multiplier feature.  In the original game if you had x15 and went for 16 it would lock.  2 and 3 had it, but I don't know the exact value.  In thps4 they make it soooo easy to lock it with jango though.  x255 is the top.  On a related note, I've landed tricks in the billions (albeit with a couple of the cheats on, the ones you buy, not codes though).  That's a cool thing. 
*EDIT2
And wobble wobble, what about mario 64?  There was some yoshi bug, kind of like the Enter the Matrix bug.  If you were too far into the game when you got yoshi it locked, or something to that effect..  I totally forget what it was (it's been a while since I've played the game.  Hrmm, I might bust it out now actually.)  That's a nintendo-made game.