We don't, but at the start, when I created the league, I kept the "classic" NFL conferences and team names. But I allowed people to change names/cites, with no restrictions, so this is where we ended up. It's more fun I think with people able to move/change. Especially since there is no game impact. I think a "road game" has the same impact whether in London or New York. The only difference is the weather - if someone moved to Alaska, they would play a lot of cold weather games and that affects the simulation.
Let's not forget that once upon a time the Falcons and Saints were in the NFC West and the Cardinals in the NFC East (and the Cowboys are still in the East!), so geography has never been a point of emphasis in the real NFL either. Even today there's that classic AFC South team all the way down in... Indianapolis? And of course that AFC West team way out west in... Kansas City.