Driving Down the 101

Kevin Drum is trying to find the answer to a question I asked him when I was in Orange County a little while back -- why is it that in southern California they use the definite article when referring to highways by number? Here on the east coast we drive on "I-95" or just "66" but over there they have "the 101." Thus far, his research isn't turning up anything very convincing. Anyone over in these parts have any thoughts? My pet theory has to do with Phantom Planet:

When I first heard this song, I thought they said "the 101" just in order to give their lyric enough syllables. Then I learned that's how everyone talks in that part of the country. But what if the band just brainwashed people into thinking they talk that way? Think about it.