The West Coast is more Asian, more Latin American, less Black, less Italian or Irish but (I think) more German or Scandinavian, in large part more recently-settled and with much more recent explosive growth, has much fewer places with a history of population decline, became part of the United States later, is less dense and has more space, has proportionally more fringe low-church Christian groups and Mormons (although this is tangential to liberalism I suppose), fewer old mainliners and much fewer non-Hispanic Catholics (see point about Irish and Italians - I am assuming "East Coast" here effectively means "Northeast Coast" as it so often does) and a whole lot of other demographic differences that do not come to mind right now. All of this relates to an extent to the gross stereotypes discussed in the thread, but is not the same thing as them.
I think though that, even by these standards, the archetypal ‘West Coast liberal’ city in a lot of people’s minds - San Francisco - shares some distinct similarities with its East Coast counterparts: an extremely strong machine-based political culture, a long history of organised labour, and a Democratic Party which has tended to be dominated by Jews, ‘white ethnics’ and African-Americans (in spite of its most distinctive demographic feature being a very large Chinese population). It is true that San Francisco is a very unique place in a lot of ways, and the oldest major city on the West Coast (which probably helps to explain in part its more ‘East Coast’ characteristics), but I still think these similarities further highlight the difficulties in making the conceptual distinction that this thread attempts to.