That may be true, but I've seen several TV's that differ in viewable area.

Yes. Set-top boxes and other gadgets whose user-interfaces are meant to be viewed on TV, have to restrict themselves to the "safe area" which means cutting off 10% of the full 4CIF (or QCIF, can never remember which is which) display resolution. IIRC the 10% is a very conservative figure, though, especially for modern TVs.

Peter