3D and VR are two different beasts. Moving your head while playing a 3D game (or watching a movie) doesn't affect the scene. There's no motion sickness to be had (besides a very small percentage of the population which actually do manage to be affected). When it comes to VR with head-tracking, you need another level of speed and fluid motion entirely. I've used the DK1 and own the DK2, and I can assure you there's a world of difference between playing a game that's been properly optimized to play fluidly on it (eg, Elite Dangerous) and playing one that hasn't been (eg, Portal 2). Within 30 seconds of playing Portal 2 with the DK2, and I had to turn off the PC and lie down from the motion sickness. (No, not from going through portals - hadn't even made any - the engine just wasn't "right" for it).
You're right, you can do stereoscopic 3D on an onboard VIA chipset with a mobile processor. You don't suffer if there's any frame lag. put, but it into a headset where the scene moves where you look, and you'd suffer. Their original goal was to get frame lag down to under 19ms for head movement updates, but I believe the goal is now something like 9ms. That is, in less than 9ms after a head movement change, it now needs to have rendered the first frames it wasn't predicting and have calculated the speed and direction of your movement so it knows which frame to render next. It's not like a mouse where you've moved it to a precise location and the engine knows already exactly what frames are to be rendered next. You're organic, and it's using accelerometers and infrared head tracking to measure as carefully as possible (without the pinpoint precision that, say, a cursor or controller button has) exactly how you've moved your head, and correctly predict (it already needs to be rendering the frame before it flips it, because by then your head's moved again) what the next one's going to be.
This all has to come together to give you a fast, seamless, fluid natural motion. And to pull this off with modern games at HD resolutions (neither DK1 or DK2 are "high definition" by any stretch of the imagination, which is the only reason they get away with fairly reasonable feeling - even though sometimes jerky - motion for games that are specifically optimized for them) will require a good video card and a good processor, because the average consumer wouldn't (and shouldn't) accept the image resolution of the development kits.
A fixed viewpoint 3D render like you're discussing is much "cheaper" processor-wise, and even when it stutters, doesn't make people sick, hence not needing a powerful videocard.