QUOTE(griffin XXI @ Sep 12 2006, 04:18 PM)

Not to seem too much like doofus, but are saying the attach rate is greater than all others in their first 9 months of shelf life, or since their inception til today?
Inception till today... but if you looked at only the first 9 months typically the first year attach rates are substantially LOWER then they are across the console's life span (because the consumer took a hit buying the console and accessories also because there are less titles to choose from so there is typically less that interests them), so in terms of just that the Xbox 360 would just beat them but KILL them if you just looked at the first nine months... most consoles are lucky to have an attach rate over 1 or 2 for the first year.
as for nickthegreat's comment, you're right that install base is important but it's no more or less important then attach rate...
Basically the install base is how many people have the console (obviously) and the attach rate represents their willingness to buy new games.
You could have an install base in the billions but if the attach rate is barely over 0 chances are you wont sell a single game.
Similarly if the attach rate is HUGE but you've only got an install base of 10 consoles chances are you wont sell very many copies either.
Simplifying the equation you could probably say
install base * (attach rate/number of games on the market+1) = the likly number of games you'll sell
Obviously it's FAR FAR more complex then that with market trends and genre saturation, time of year, etc. But that's assuming all games are equal and the market works in a linear fashion.
IIRC Sony's PS2 had an attach rate of about 2 games last gen... the Xbox had about 4 and the GC had the best attach rate with around 6 I believe. 360 currently has about 7 or 8.
Lets run some numbers shall we? Number of games on the market would mean number of games currently and readily availble to consumers Xbox 360 has about 80 games excluding XBLA titles (based on the list on mygamercard.net) the PS2 has a library of about 6000 games world wide but only 1/3 of that is availble in the US/EU. Also lets assume that only 20% are currently availble at any one time. Most stores wont stock the entire catalog and after a while most of the non best-sellers stop production and dissapear completely (meaning that game is no longer on the market)
so for the Xbox 360
~6 million * (7/~80) = ~525K
for the PS2
~130 million * (2/~400) = ~650K
So you'll see, even with the incredibly small 360 install base, due to the low number of available games and the high attach rate a publisher can more the likely come close to selling just as many copies on the Xbox 360 as they can on the PS2 TODAY... this is why you see a lot of Xbox 360 games in the best seller lists right along side their PS2 counterparts... it's because of the high attach rate at such an early point in the 360's life.
Obviously these numbers are in no way accurate and most of it is just guesswork but I'm just trying to get across why attach rate can be just as important as install base.