I think this is an example of the same kind of thing as standing "on line" -- you can do it in NYC, but if you're outside of Manhattan and you say it, you've pegged yourself as being affected. And the NorCal/SoCal schism means anyone who says "The 101" up here gets their azz kicked, pronto :-)
And what about those Canadians who are always "in hospital" and never "in the hospital" ...?
(Though I hear they have to wait 3 months!)
/jordan