I think in this case, it is the size of the TV and the weight. I am thinking not too many people would be looking to mount a 58" TV to the wall, it weighs in at 136lbs.
Just did some checking and it seems many of the wall mounts capable of handling the weight are also non-vesa able as well, so it seems to be no big deal whether or not a TV is Vesa compliant.
Last edited by jakewash; 02/10/0908:34 PM. Reason: added some info