I've met several people whose first exposure to roleplaying was online. I've seen more than a couple people say that there were only able to find the enough people to play their game of choice online. I probably wouldn't have gotten so into RPG's in college were it not for the internet making games and discussion so readily available. Consider the resources of the average gamer now versus pre-internet, just about anything you'd want to do with a game system has probably already been done an posted on the net by someone.
None of this is specific to DnD but as the most played game out there, I'm sure it cannot help but benefit.