Ah, so that's why :P

Yeah I think I know what you mean about the hotspots.  I never actually tried rear-projection when I had my Epson (not enough room), but I'm guessing that's why, on rear projection TV's, they have those fine radial grooves embossed into the screen.  Probably to scatter the light more evenly across the screen and prevent the hotspots.  As soon as you said "hotspot" I thought of those radial grooves!