Obviously Sony has a big stake in 3D. They have their own TV sales to think of, and PS3, TV, and 3D games sales feed off each other, so it's natural they take a more proactive stance in this, and tout to the wealthier early adopters. Microsoft has no such thing, so it's a natural stance for them to let the dust settle first, and wait for mass-market adoption to make a 3D effort monetarily viable. Plus, I know this from limited personal experience, but i'm willing to bet it's a significant phenomenon: many households have a PS3 for the added bluray functionality, which means that a significant chunk of PS3 owners are more on the side of home theater enthusiasts, being more prone to early adoption of 3D.
If and how 3D will become mainstream is anyone's guess. If i'm to take a shot at it, i'd say it will, but not necessarily in the form or forms we know today. If past developments have taught us anything, is that this particular market has been allowing no time whatsoever for any standard to settle for long, and i doubt that tendency will change: manufacturers are always trying to put something new on the market as fast as possible, it's simply a tried and proved business strategy. PC hardware, TV's, Mobile devices, etc., everything gets old fast. And even faster if there are icky details that limit mass appeal, like needing a sweet spot to view 3D (3DS a bit exempt from this given its size) or needing added cumbersome accessories like the glasses. In the long term, this will not do. It will do enough to be profitable, but likely not to reach true mass market. Or so is my guess. What's next? Holography? Volumetric displays? Who knows...