The other thing to consider is the lack of D&D type adventures left in this world... There are very few "Lost Cities" left to explore, few ruins, and those ruins are not usually inhabited.
While villians do exist, it's difficult to put yourself into position to do something about it. OBL and Ayamin al-Zawari(sp) are well protected and have physically isolated themselves. While they may well be hidden in a fortress somewhere, finding a secret entrance is not as easily done as it is "in game."
Also, we have become a world of rules and "Mother May I?" There are several accounts when various "villians" have been in the crosshairs of "professional adventurers" (CIA operatives, etc), but permission to pull the trigger has been withheld. D&D adventurers have no such limitations.
While "Adventurers" do indeed exist in modern day, direct correlations to D&D adventures don't really exist any more, if they ever really did. There are few dungeons to delve, few caves to be cleared of kobolds, few Underdark civilizations to be rooted out, and few snake-men sacrificing virgins to summon demon-gods to be eradicated. Tragically, we are left with terrorists, skinheads, bail jumpers, street gangs, con-artists, Nigerian businessmen with money transfer schemes, environmental pollution, global temperature change, and other assorted riff-raff and problems. No Smaug, the Greatest and Chiefist of calamaties, no Zargon resting under a city, seeking sacrafices, no Ring ro be cast into the fires of Mt. Doom.
I think that it's because of these types of problems is why we NEED games like D&D. It's nice to be able to actually solve a problem for once, be the hero.