First, on a TV you'd be hard pressed to display more than 640x480. There are just not enough lines in the TV standard to support more than that. And IMHO 640x480 is a bit passe right now. I already know of games that won't even work at all under 800x600 (e.g., "The Sims"). Heck, even for web browsing there are many sites out there designed for 800x600, or even for 1024x768.
Also, TV refresh rate is 60 Hz interlaced for north America, or 50 Hz interlaced for Europe. That boils down to 30 or 25 Hz, only split into alternating frames that draw only the even/odd lines. It's enough for viewing large blobs of colour from a distance, but you don't want to focus on small details on that one. (E.g., on the letters when editing something.) Ergonomy says you need at least 75Hz, NON-interlaced, for reasonable eye comfort. (Or to reuse an old cliche: don't do that. You'll go blind
)
There are even more limiting factors than even that. E.g., your average cheap TV has been designed to display images with relatively smooth colour transitions. It doesn't need to have mondo signal bandwidth, like good monitors do, for sharp edges.
------------------
Moraelin -- the proud member of the Idiots' Guild