I can't answer this question without pondering on the PlayStation2.
I think, to a minor extent, it is a number of factors including entry price, a software library defining the "experience," marketing, big name titles and on.
Learning from the PS2, I am convinced it comes down to multi-media functionality with a new technology that is becoming mainstream just as the system is being released. Case in point, the PS2 was released just as consumers were transitioning from VHS to DVD. Henceforth, they could kill two birds with one stone:
1. Their family's gaming wants and 2. The parent's home movie viewing wants
Well what about the PS3? The PS3 with Blu Ray when it was launched failed in anticipating the world-wide adoption time from DVD to blu ray. They overshot by about 5 to 10 years. Just reading from VGChartz posts, Blu Ray still has only about 10 to 12% of the home movie market and the technology has been around for coming on 5 years now. The PS3 even currently is ahead of it's time, which will be good when we are old and reminiscing, but being ahead of your time does not pay the bills for the development costs.
So for me, it comes down to multi-media functionality that advantageously employs new technology just becoming mainstream.
Mainstream and widely adopted I considered synonymous.
