Achivements can move up to 40,000 copies of a game.

[Ail]

trophies are the same they do move units of software.

I do not purchase a game depending on whether it has easy trophies or not but I will purchase a game with trophies over one without them....

This has made me played some games I woudn't have played otherwise ( and I was happily surprised by quite a few of them).