I may be wrong, but I'm pretty sure that the 60" refers to the screen size (Top corner to opposing Bottom corner). However, many TVs have varying width screen surrounds depending on what they house such as speakers.
So surely the measurement that you should be looking for is the actual width of the TV, which I'm sure will be given on the TV's specifications.
No you're not wrong about the screen size measurement....all specs checked...55 = 1228 mm, 65 = 1449 mm width.
Slap bang in the middle is where I'd ideally like to be.......about 1338.5 give or take a few mm.
Currently have a 50" Plasma so as Kryton says 5" doesn't make a huge difference, but 10" would.