For achivements its not bragging rights that are the driver, its some strange feeling that you're accomplishing something when you really aren't. Playing Warhammer in beta for instance (why my trophies are sorely lacking, WAR is to blame....well and being too lazy to add the Uncharted achivements on the site that updates my tag) I found myself doing extra quests, exploring and undertaking activities I normally don't undertake in MMOs just to get unlocks for the games tome of knowledge. Currently noone can really see in your tome (except one achievement you can display in the form of a title like being killed by an enemy Chosen class gives you "The Chosen One" as a title) but that doesn't stop them from being addictive.
Ditto for trophies, there is a really sense of accomplishment when one is unlocked ,especially the harder ones. It isn't as if I play JUST for that, but it gives a reason to play in a more through manner and provides rewards for not giving up at certain junctures. Trophies are also better then achievements in way since they are given more individual meaning through the leveling system (instead of just points). It is hard to explain WHY a leveling system seems to matter (say getting a gold trophy that puts you to a lv 6 gamer level) then getting points (100 points for finishing game X) but never the less it seems to be the case for a lot of people. I think it relates, again, to goal oriented thinking.
What is the goal for a gamerscore? To get it higher right? But to what end? For the trophies the goal for getting the next trophy is to get to the next level. Leveling, in almost any genre, has shown to be the best motivator in all of gaming. Hell even FPS games have levels now (played COD4 lately?) they could just as easily have done call of duty points ;).
PSN ID: ChosenOne feel free to add me
