The Apple specs say specifically "FaceTime HD camera", which seems to suggest they believe transmission of HD chat videos is possible http://www.apple.com/macbookpro/specs.html
Also, who says I prefer framerates over picture quality? Perhaps a reduced framerate is the better tradeoff in exchange for high definition images.
You would need an upload speed of around 5Mbit/s to upload HD video (720p). Less for lower quality of course, but then why are you doing HD in the first place? It's doable, but not realistic for most people.
You also need a monster CPU to compress video that much in realtime. With a slower CPU you'd get worse compression and need a faster connection (or lower quality).
Reducing framerate doesn't help as much as reducing resolution because little changes between frames, so there anyway isn't much to upload. (You either upload a lot infrequently, or a little frequently. It doesn't matter a ton. You get some benefit, but not much.)
A small tablet probably doesn't have the CPU power to compress an HD stream, but a laptop should.