I'm not a fan of D+D, as I said, I only know who he is from a guest spot on a TV show. But I have played other RPGs and roll-based games, and I agree that his idea kept a lot of kids out of trouble- despite the idiot parents thinking their kids were "satanists" who were getting together to "worship the devil". Its amazing how many folks I've worked with or known otherwise who admit to being ex-RPGers at some point, and all say it was probably the safest and sanest way they could have spent their time.
RPGs are misunderstood by a lot of people who don't play them, but they've been very popular for decades now and between the games themselves and the computer and literature spinoffs, they're a multi-million (if not billion) a year business. They'd probably still be around in some form, invented by somebody else, but his system is the one that almost all modern ones trace their lineage from.