I've had many insist on knowing how much experience I have with HTML 5, as though my previous experience with HTML 4 has no relevance. I don't know why the talk

I've had many insist on knowing how much experience I have with HTML 5, as though my previous experience with HTML 4 has no relevance. I don't know why the talk about HTML at all, a half decent programmer that's never done web development could learn all they need to know about HTML in a day.