i measured the difference adjusting it to the way i had and to the size it would take to make it the right aspect using a square Adobe PS. the difference is this:
5 3/8th inches wide
5 1/16th inches tall
when adjusted to make it a perfect square on the monitor there are almost half inch gaps on the left and right of the monitor.
so, what you have to ask yourself is, "What difference does 5/16th of an inch make?"
when dealing with presice measurements, your not going to be eye balling it (CAD stuff) and when doing normal design or art, i dont think that much difference is going to ruin anyones work. its like when im drawing, i may twist and turn the paper (not supposed to but anyway) causing the to be slight distortions in my perspective of what i want to draw. happens all the time and unless you walk around with a ruler, i doubt will ever notice the skew factor that in everything that has been done by eye.