we like to play games other console owners don't.

That's true. At the end of the day, we're just Too Human.

Achievements obviously play a big part, and theres so many more games on 360 that have online multiplayer that you find yourself keeping hold of them for longer and longer (or even keeping them forever)

Example, these games all have multiplayer and i doubt i will ever sell any of them in my collection

Gears of war
Gears of war 2
Halo 3
Virtua tennis 3
Left 4 Dead
Smackdown vs Raw 07 (It owns sd v raw 08, i aint played 09 yet but will soon)
Tony hawks project 8
Virtua fighter 5
Project gotham racing 3
Project gotham racing 4
Crackdown
Forza motorsport 2

Then theres certain XBLA games that for example Sega fans will keep coming back to.

Sonic
Sonic 2
Golden axe
Streets of rage 2
Rez HD ect.

Basically what im getting at is that online is king this generation and no other console out there has the sheer amount of games that offer multiplayer when compared to the 360.

Annoying people on your friends list that keep sending you invites until you break down and buy the game.

 awesome games...

Library, community, quality, price of older (superb) titles.

the community.. I guess when you see all your online buddies playing a certain game you can't help but be swayed to join em'

I think it is a combination of XBOX Live and Achievements. I know when I pull up my friends list (which is very fluid in LIVE) and I see my friends all playing a particular game, I want to go out and buy it, and then pass them up in achievements. I think it's the competitive nature of man.

People who own the system buy alot of games for it.

it's just the demographic that goes out and buy the latest thing.

can't expect that from kids and grandmas.