I realize this is a newly resurrected thread, but I figured since its at the top again Id chime in.
I always assumed women couldnt do push ups and chins because they weren't expected to. I mean Ive never really paid much attention since high school but they always allowed them to do the girly push ups. Of course you are never going to do normal push ups if you dont try.
Of course, I also thought it was silly that they were getting coddled. I know they don't have as much strength, especially if they arent training, but they dont usually weigh as much either. I think it kinda balances out.
As for chins. I dont think I can do them very well myself. Granted I havent really done them recently since its hard to find them high enough that I can actually hang from without hitting the ground... but stronger i get the more i weigh so its not like its been getting easier to do them. Maybe ill try them one of these days.