Hey, speak for yourself. In theory, I could plop a few cheap grippy foam sleeping pads on top of my beloved Subie, grab a summer bag, and clamber right up, being the not-quite-mythical 50 kilogram woman. Now, I wouldn't try jumping up and down on the roof, but the weight distribution of a prone human should be no problem for any hard-top car.
Concerning sun/moon roof that opens wide enough to stick your head and shoulders through: Does anyone actually kneel on seat and stick the camera operating end out the roof hole to photo birds? Plenty of people roll down their windows and effectively use the car as a blind. If you can shoot out the roof hole and the birds ignore you, a sun/moon roof might be worth the money. I have never had or wanted a sun/moon roof, just decreases the interior height and sense of spaciousness. I'd make an exception if I could actually use the fancy-schmancy roof for photography.