Sure that's a factor, but it mostly is because microsoft is the only company thinking long term about the game industry.
Nintendo as usual has shot their load early. Luckily it was such a marvelous blast that they can ride it for a while. Wii Sports Resort wasn't a system seller. It could have been. It should have been. But they don't care anymore. And yeah you can make the weak argument that "people who would buy this would've bought the wii earlier." That's nonsense. These NPD numbers show that over 500,000 people bought consoles this month that they most likely did not own before. 500,000 people finally pulled the plug in the middle of july. There's lots of persuasion still needed this late in the game to get people off the fence. WSR should have been the ultimate fence shaker for nintendo.
Sony would be thinking long term like they did in the ps1 days, but they're too busy picking up their short term mess to even consider looking down that road...which will result in more short term messes and blunders. They're at catch 22 levels of bad at this point. They gotta find something that will get them off that rollercoaster.
Microsoft is the new Sony. They're playing it steady. They keep at it a little at time, and if nintendo doesn't watch their ass (again), they're gonna fall behind in the home console market. Obviously, not this gen, but there's lots more gens coming.