I think most gamers have a relationship with D&D that's similar to an open marriage. You're allowed to see all the other games you like, and you can even bring them home sometimes, but in the final analysis there's only one truly lasting love - and that's Dungeons and Dragons. The other games are fun, and they add a lot of spice to your life, but D&D is the only one that feels like home.
It's only by virtue of the fact that D&D is usually the gateway to the hobby, of course. And for people who came to role playing through other systems, I guess it doesn't apply. But I'd estimate it's true for 75% of gamers.
So I miss D&D when it's not around. I'm running a weekly Cyberpunk 2020 game at the moment and really enjoying it. But that hankering for hit points, THAC0, orcs and random encounter tables won't go away. In fact it's growing stronger. I'm not sure how much longer I can take it.