> If they're not the same, then they're not inches.

I'm not saying that UI elements should necessarily be the same size, but the option should be available. Having a point be equal from display to display doesn't mean that relative scaling isn't impossible; it just means that you need to use different units for those cases (which is probably most of the time). Points really aren't all that useful on computer monitors at present; you're better off using EMs, percentage or possibly pixels depending on what your goal is. This leaves a gap, however, when it actually is advantageous to know for certain what size a UI element will be at display-time.