My guess is that the viewable area on a TV goes much further into the corners of the tube than on a monitor

That may be true, but I've seen several TV's that differ in viewable area. One Zenith in my house seems to have decidedly more plastic over the edges of the screen, enough so that station logos are right to the edge instead of spaced a bit.

Of course, it could just be that I have an older TV. I also don't know what size it proported to be.