Quality =/= sales

[Signalstar]

This is a bad comparison. The two games are only available on platforms with different gaming preferences. They never had the opportunity to sell to the same audience. Gran Turismo is available to a userbase that prefers racing games in general. The PS3 has sold more racing games with much less titles so the average racing game sells higher than on the other console.

PS3: 74 racing games; 53.49 million sales
http://www.vgchartz.com/gamedb/?name=&publisher=&platform=PS3&genre=Racing&minSales=0&results=200

360: 87 racing games; 50.13 million sales
http://www.vgchartz.com/gamedb/name=&publisher=&platform=X360&genre=Racing&minSales=0&results=200

A better pure example would be GRID vs. Need for Speed Undercover sales.
-Both games came out on both platforms in the same year.
-GRID has a significantly higher metacritic score than NFS (more than 10% higher)
-Yet NFS Undercover sold better on both consoles.

GRID
PS3 Metacritic: 87
360 Metacritic: 87
PS3 Sales: 1 million
360 Sales: 830K

Need for Speed Undercover
PS3 Metacritic: 59
360 Metacritic: 64
PS3 Sales: 1.88 million
360 Sales: 1.48 million

This example is a much better demonstration than the very flawed one featured in the OP but I assume it is overall much less satisfying for him.