JohnS47:
Its called acting for a reason!
Never heard of method acting John? and as Tiptopper says it's possible a few directors demanded the real thing.
SNM:
Dude, they're not porn stars. They don't share our fetish (usually). Do you think action movie actors get real cuts and bleed real blood when their characters get hurt? This is no different.
Absolutely, there are countless occasions when actors have been hurt for real while filming fight scenes or carrying out their own stunts.
I also don't think a spanking handed out in many of the older films would be considered as porn, just a normal day to day practice.
I was just wondering if some actresses would have decided it wasn't worth the hassle and told their co-stars to just go ahead and do it for real.