Of course. And, as I said, I'm not trying to rain on anyone's parade.

Just being nostalgic and holding a grudge, :D.

It seems the game isn't selling like the initial expectations. I guess this game more than any other proves how the Xbox 360 and PS3 shared the PS2 userbase fairly evenly. The sales are still great however and I believe that their next game ought to surpass this by a large margin given the opportunity to release it much closer to the launch of the PS4.

The game deserves it. Sony has worked hard to improve it since launch.

i stopped playing it after about 3 months and i've heard its like a different game now to when it first launched. what exactly have they added or changed? i might start playing it again soon.

GT sold 25M on the PS2 and it sold 8M on the PS3 if we consider full versions only. The PS3 sold 67M copies and the PS2 sold 150M copies so the attach rate is pretty steady at around 10 Playstations sold per GT game sold. So yes GT is selling at the expected rate but the expectations for the sales were still too high. I remember there were many predictions that it'd have sold more than this by now and anything under 10M was considered blasphemy. So yes GT is selling as expected and it isn't selling as expected at the same time.

Outliers are gonna exist in any prediction from both extremes of the spectrum. It makes no sense to use outliers as a means to judge the performance of a game. The average prediction for GT5 was around 10-11 million at the most - a figure which should be reached.

In fact, in this thread, the average LTD prediction was only 9.34m 

That prediction will only hold so long as another GT game isn't released.

Anyway:

GT1/2 PS1 Sold 20M copies over 104M units.

GT3/4 PS2 Sold 26M copies over 154M units.

GT5 PS3 sold 8M copies over 67M units.

The performance of the game seems right on target given the fact that there has been only one GT release this generation. If there isn't another GT game released this generation then the sales of the overall franchise will be substantially down over the previous generations so either it will meet the expectation of franchise sales or it will meet the expectation for individual title release but almost certainly not both.

Woot! 10M is achievable :)

I'm not sure what you're trying to prove with those numbers. The lowered franchise generation sales don't accurately represent much of anything of relevance. It's directly correlated with the frequency of installments which diminshes the importance of the size or selling-power of the franchise. Those figures don't paint an accurate picture for how the public views Gran Turismo; it shows how many installments Polphony Digital has been able to produce.

Moreover, I don't think anyone expects (or has expected for many years now) generation sales to be near PS2/Ps1 levels with the knowledge that there would only be one mainline Gran Turismo game. I guess you could go back to the 2006-2008 era where people may have believed that there would be more than one main installment. You could make the point that the expectations of those people will not be fullfilled. That point would be completely true, but it would be of very little value, because most people discarded those expectations many years ago. You are disproving an expectation that no one holds today and that hasn't been held in quite a long time.