I find that when I'm running games set in the (ostensible) real world I have a strong desire to tie in parts of the real world to it. Players in my various V&V games are well familiar with my decision to set the games almost exclusively in the 1980's (or flashbacks, or time leaps forward) because that was when I started playing with the world. This gives me a lot of real world events to tie into, the ability to have people invent 'super tech' that's actually late 20th/early 21st century tech, and various other advantages. While I might lose some current world opportunities I think it's a pretty fair trade off. If I were to start a new supers universe I would likely have it run from late 2001 to 2012 to have the same effect - a decade where we know what major things did happen so everyone can see the effect the PCs (and other super-heroes) have on it.
Likewise when I'm setting something in an established genre property (not just aping the feel for it, as i have in the first two campaigns here) I get pretty obsessive about working within the lacunae of the canon (to give the players maximum freedom of action within the setting without violating 'history') and explaining away violations of same when I have to in designing compelling story. The players in my Star Trek (Christopher Pike era) and Marvel Super Heroes (X-Men circa 1984) will doubtless attest to this insanity.
I'm not entirely sure why I do this. I think in part because my own sense of history is tied in to the fictions that I read set in and around history. Yes, I can tell the real from the fictitious, but it came to mind Monday when reading about Margaret Thatcher's death. My first image of her was not anything from her 'real' history, but her five panels in Alan Moore and John Totleben's "Miracleman". In my head it's all of a piece.
Gaming did this to me. Gaming and comics. And TV. OK, maybe I was like this already.