I never thought about it before, but this is so true. It even extends into other game genres.
For example, one of the NPC NCOs in our Modern military game is an eighteen-year veteran of the Foreign Legion - he's served in every major campaign of the Legion since 1938, and when one of the characters has a question about the Legion, the standard response will be, "Talk to Sergent Verdurand" - if it's about something that happened during WWII or in Indochina, there's a good chance that Sgr. Verdurand was there, and it if happened from about 1890 on, then it's likely that either his grandfather or father were there, as service in the Legion is a family tradition.
Hmm...Sgt. Verdurand as Gandalf. Too funny!
And yes, my fantasy games include the archetypal wizened sage, but the setting I'm working on, there is a twist: the sage of the setting is profoundly evil, so in this case, it's more Saruman than Gandalf.