I was raised to understand that swearing is the result of an inability to express oneself using better terms.
I've never felt comfortable swearing in front of my parents, really. When I was at the age where I was most likely to fly off the handle and start cursing them out, I knew that it was much better to just avoid communication at all instead. I mean, I COULD curse out my parents if I really wanted to, but now-a-days the desire just isn't there. They pretty much only want to help me out and be helped in return. When your parents treat you as a peer instead of a child, you basically don't resent them anymore.