Well speaking for myself... I've never seen any Beyond 2 Souls advertisement until now! Only seen the premier thing* on the movie theater and the trailers at the expos (which mostly only hardcore gamers watch)... And a lot of ads for Wonderful 101, IGN was full of it! Every video was sponsored by Wonderful 101 and look at it's sales... Also Zelda Wind Waker HD had a lot of ads even VGChartz became dominated by it for some days!

Reviews suggest that, despite the big stars, it's not a AAA game.  Also, as a generation draws to a close, there are TONS of other options for the gaming dollar. Many of us predicted that the game would do sub-Heavy Rain numbers ages ago.  Games like this don't have million sale first weeks.  I think it will top out at 1.5 million which is respectable.  Of course, while a million is the benchmark we've set for ourselves on this site as "success", we've also seen games that sell several million be labeled as failures (ie: Tomb Raider and Hitman: Absolution).  It would help me if you could tell me the budget of the game.

I think it's mix of the two.  Your userbase becomes more diversified as it increases, no question.  But many sequels decline with each iteration.  But you also see sequel increase in sales with userbase if they remain popular (COD, GTA, etc).

I think you should avoid exclusive titles when looking at attach rates because they often are unique titles.  A great game to look at is something with consistent interest year over year.  I like Madden on X360 for example.  From '06 to '10 sales increased every year until it peaked at about 5X year 1.  They then experienced a modest decline as gamers begin to experience apathy with their old system.  The increase is not consistent or linear.  There are many factors such as the titles that early adopters prefer.  But there is no question that if a series has consitent interest sales will increase signifantly and measurably with userbase.

And yes, W101 is a much bigger flop than Beyond.