This thread has been approved by Radishhead. This thread isn't a Gran Turismo vs Forza thread, this was just as an example. It's acceptable to talk about these games in context of the original question ("does quality = sales?") but if it turns into a Forza vs GT flamewar then it will be locked again, and suitable moderator action will be taken against those responsible.
I've just discovered something shocking while browsing through the vgchartz database...quality does not equal sales, and I have definitive proof. Forza and Gran Turismo are the best examples I can use to illustrate this phenomenon because they're both their respective consoles flagship exclusive racing franchise.
Anyway, lets look at quality first. Here are the metascores of all the Forza and Gran Turismo games released this gen:
Forza 2: 90 metascore
Forza 3: 92 metascore
Forza 4: 91 metascore
Forza average for this gen: 91 metascore
Gran Turismo 5 Prologue: 80 metascore
Gran Turismo 5: 84 metascore
Gran Turismo average for this gen: 82 metascore
Given that Forza games are better than Gran Turismo games and there are more of them, any rational person would assume that Forza has sold more than Gran Turismo... But that's not the case. Here are the sales:
Forza 2: 3.99m
Forza 3: 5.11m
Forza 4: 2.43m
Forza total sales for this gen: 11.53m
Gran Turismo 5 Prologue: 4.11m
Gran Turismo 5: 7.97m
Gran Turismo total sales for this gen: 12.08m
That's right folks, despite Forza being a higher quality franchise and having a higher quantity too, it has still sold less. What the hell?! Startling, to say the least. Can anyone explain this phenomenon?