There are TVs that are great for gaming, with low input lag and defeatable processing. Panasonic plasmas for example. But plasmas are not great for desktop use as you may get burn in.
The biggest difference is that with a TV set further away, console ported games are generally more pleasant because they have low field of view (FOV) so when playing with a PC monitor it feels like you have slight binoculars on. On the other hand, a TV usually has to be next to a sofa and at least I'm not particularly comfortable playing from that position with anything but a controller. It's just awkward to get a keyboard and mouse comfortable placed there.