Yeah, I've never understood charging for bags. The bag will weigh exactly the same whether I carry it on or check it.
My wife one time had a bag that was three pounds over and they wouldn't budge. So, she opened the suitcase, took out her coat, and put it on, then closed the suitcase back up. Ha. 48 pounds. Win!
I travel with only one medium-size suitcase and a small carry on (briefcase size), so it's never an issue for me. Oh, and my CPAP, which technically shouldn't count as luggage but sometimes it does.