As has been sad before you can't draw much info from sales numbers... I mean look at pop music and where the sales numbers are... do you know how many tickets got sold to Twighlight movies?
And in the case of GT5 I would say sales numbers show how well the hype sold... which was very well... even today we still have people who are just finding out about standard cars, missing damage and the bevy of other issues...
As I said before, Madden could release absolute garbage and it would be two or three years before the sales numbers dropped dramatically...
It's interesting, what I see from that video is that the AI in Forza seems more animated or dynamic somehow and that in GT it seems to be the standard "tube of cars" sort of driving... the two times the car crashed in Forza was a situation where they came two wide and the car on the left was in a bad spot, you could almost imagine the drivers face going "Crap we gotta split this idiot sitting in the middel of the track, he's going one way, I will go the other... oh crap, that's too tight, I gotta correct, gotta, gotta... oh CRAP!".
That said I rarely find these sitting still cars videos any good... what I am interested in is things like first corner pileups... I have seen collections of million Cr plus cars all smash into each other on the first tight corner of a track over and over like no ones business... I am also interested in how they respond to dynamic situatinos like a packed corner when someone spins out... all too often I end up with people drving through me when the obvious thing to do is to STOP accelerating hard, slow down a bit and drive around... but no...
That's the kind of AI that interests me...