Yes it will change with every display... that's why you calibrate it... once and only once. The only time you'd need to calibrate it again would be if, for some reason, you moved the camera.
The parallax/ depth perception is what I'm referring to that could be compensated with software. It's not that hard really. Since we are dealing with flat screens and not curved crts, regardless of the angle, we are basically dealing with a trapezoid. If you know the location of the four corners of the screen, the border can be calculated and then it's a matter of calculating the percentage left and the percentage down in relation to the borders. It's much more difficult to explain than to do actually. The only issue I can see is diminished resolution on the short end of the trapezoid.... that's why I was saying 640x480 may not be sufficient.