Gates is both right and wrong here (though of course one would expect him to present things in the most favorable light to Microsoft).
There are essentially two different types of computer users: content creators and content consumers. The content consumers are quite happy with a tablet — it serves all of their needs. Content creators either find workarounds with tablets or use a notebook (ultrabook class, most likely) which is more suited to their needs.
But content consumers dramatically outnumber the creators.
The Surface (Pro) tries to bridge the gap between tablet and notebook — how successfully will be judged by the passage of time, not by any predictions we make here. For my own purposes, I’d much rather get an ultrabook-class (as a content creator) while my wife wants a tablet because she’s a content consumer first and foremost (while she is an active blogger, she actually prefers working at a desk to do that... organization thing).
If I absolutely, positively had to have a single machine to do everything and it has to be Windows-based, the Surface Pro would be very attractive. But a smartphone and ultrabook is the way I’m looking, because I don;t have those constraints.
All I want is a unit with a billboard sized hyper resolution full 3-D display, a comfortable full sized keyboard, with a numeric pad, a wireless mouse, and input tablet/3-D mouse, rilly fast processor, immense memory, intuitive interface, hella fast connectivity, surround sound, pizza oven and soda dispenser, and I want it to fit in my pocket and pocketbook...