The 360 attach rate is higher because....the console has been out longer....

Multiplat are better on xbox and they have achievements.. i dont know why but ps3 games looks darker and blurry.. i always make comparisions.. always!.. my only complain with the xbox 360 is the poor quality hardware..

According to VGChartz data the 360's average months of ownership is about twice that of average months of PS3 ownership at this point.

So software selling equally well amongst the userbase over the years should show about twice the amount of games sold on the 360 than on the PS3.

This is due to the 360's headstart, but also due to having many new console sales dragging down the average months of console ownership. (People usually take time to build up a software library, they usually don't buy 20 game immediately and then never buy a game again, for me it's about 6 high profile full price games a year). If new hardware sales drop significantly while software sales remain steady this would boost attach rates over time.

For the US we know YOY hardware sales for the PS3 increased dramatically (relatively dragging down the average months of ownership).

This is true. I agree but at least some of the 360's attach rate can be traced back to the fact that their is more incentive to buy it on that system. 360 games all have built in achievements which play into a larger game of who has more points then you. MS also shells out millions of dollars to get exclusive content for multiplat systems (50million to be exact in GTAIV's case). I believe small things such as these sway even a few's decision on which console to buy games for.

Achievments are both good and bad.

They are fun if they aren't ridiculous (getting 10000 kills in Gears of War...). If you really enjoy a game you will do the achievements, If you just like a game you will probably skip most of them, if you still want to get them all in a crappy game, you have problems. Achievements can ruin online games as well, 1/3 Halo / Gears matches i get a bunch of people who want to "trade" kills just to get achievements, that isn't fun if you ask me. Then you get people who will only use because they are after a certain achievement.

A lot of times I make my own "achievements" for Wii games, in Zelda I always try to get all 20 hearts, do all the side quests, get the best score in mini games, etc. In Metroid I go and find all the upgrades, get every last scan, do all difficulties.

I got gamefly and I bought madden 09 and GTA4 COD4 PS3 version all for $45.00 ea. and the week they launched GF is good for craptastic games and easy achievements but the games at a discount is cool too. having all 3 systems wii 360 PS3 paying $30.00 per month tot have 3 games out at a time is way cheaper then buying them all. and if its a true gem you keep it.

I have 40,000 plus gamerscore and got my console at launch. I have a riend who got his a year after me and owns double the games I have and over 50,000 gamerscore he downloads every xbox live game too. if he cant get achievements halo3 cod4 he wont play online if hes got all he can get.

PS i got my first trophies on warhawk the other day (:

The collective userbase and achievements do help with attach rates, but getting the games for the achievements, also boosts the used games market, since you're more likely to sell the game after getting the achievements if you got the game just for your score. Also, adding the replay value, is going to keep you from buying new games for longer.
Anyway, as someone already said, on monthly basis average, Wii owners have bought the most games per console.

So the secret behind 360 attach rate is its extra year in the market.