I believe what you see as "momentum" comes from meeting the demands of a market better than an opponent's console. The measure of this is reduced to sales, which is about the only way we track things. If a market is at a saturation point, things tail off for a console.
As it is now, the PS3 is slowing down some SALES WISE, but it still leads in the world over the 360. In North America, the XBox 360 is still leading in sales. However, it is trailing the Wii. It continues to trail the Wii, and hasn't led often in sales worldwide over the Wii. As far as generating it being the perception of being the top console you have to get, the PS3 lost that to the Wii, and doesn't appear to be getting it back at all. If there is anything "momentum" as in an aura that makes it feel one MUST buy it, because it is THE thing, it has to start beating the Wii on a consistent basis, and it isn't there yet.
To sum up, I say that people DON'T buy consoles due to something called "momentum" (unlikes sports teams that can get in synch and perform at peak and continue to win). Momentum is for vehicles, sports teams and armies that can roll over an opponent. A marketplace is far more of a dance between a company and consumers, where you be agreeable to them, so I don't see there being momentum at all. I do see a company needing to be a leader in capturing what customers want better than the competition though.
I think people here would be a bit surprised to find that the rest of the world doesn't even remotely share the same set of values on here, or feel the same way as people on here about things. Most could care less about how the consoles are selling, and don't take any form of pride in any way from the place a console is in saleswise.