Yeah, I read this when if was first posted on Engadget and came away with the same basic impression you did. My take is that it isn't the OS that needs to change. What needs (well, needed) to change is the mindset that a metaphor that works for one form factor or for one use can/should be adapted for use in another. This was Microsoft's #1 mistake with both TabletPC and with PocketPC and the mistake I think Apple made with the iPad.
I think the desktop OS is great as is. Of course evolution will continue, but I'm not certain we'll see a revolution any time soon. It is too refined and well suited for the form factor. Power usage needs a flexible interface (layered windows) and precise methods of input (i.e., the keyboard and mouse). Xerox PARC got it right early on and Apple and MS have done an admirable job of advancing the concept over the past two decades.
"True" laptops are really just mini-desktops these days. I don't see much change happening there beyond perhaps some touch or better multi-touch integration into the trackpad to better approximate the precision and speed of a physical mouse.
Perhaps a "true" netbook should be something closer to Jolicloud with a little touch added since the precise control of a mouse is less of an issue for a device dedicated to casual computing. I DO think that window management needs to be different on a screen of this size.
A tablet/MID, well, certainly NOT the same metaphor as the phone/PDA.
IMO, something of a mix between WebOS and Origami is probably correct. However, I'm pretty certain that Apple got it correct that a tablet does NOT need to be built using mobile PC parts but rather can make due just fine with mobile phone parts. Do we SERIOUSLY want to do video editing or even heavy document creation on a tablet? No, it is about media consumption and perhaps note taking--needs a stylus for this, IMO, though as people migrate away from handwriting, I'm not sure this will continue to be a function naturally suited to a tablet. Incidentally, if you DO want to do video editing, then this is where you'd likely offload most of the processing to a PC and just use the tablet as a fancy, mobile input device. Hmm, this is a really neat idea for a whole new class of apps...
As for the phone/PDA, well, probably what we are seeing now with iPhone/WebOS/Android. Kudos to Apple for figuring this one out and for the others for continuing to innovate in neat ways. Can't wait to see what Microsoft adds next month.
There is likely not a single interface that is one-size-fits-all even at a form factor level. But I'm sure similar, best-of-breed metaphors will emerge (like the finger-flick and pinch-to-zoom concepts for phone/PDA's or the mouse and double-click for desktops). But it is certain there will be major differences in the metaphors that work across form factors.