I usually had stirrups in the US, and I actually did find them quite comfortable, so long as they were covered with something and I wasn't putting my feet on metal bars (one doctor stuck oven mitts over them). The pose itself really felt quite relaxing, I have to say.

I wonder if any of it's a modesty thing? When you have your knees up and a sheet covering you, you can't see what the doctor's doing down there.