[poulsbohemian]

While everything you wrote is basically true, there's perhaps another detail of Washington and Oregon politics to consider - the west and east are completely divided politically in both states. For example, if you were to look at another divisive issue like the legalization of marijuana, you'd probably find that exactly the same counties in Washington voted against it as that voted against same-sex marriage. Eastern Washington and eastern Oregon are rural, agrarian, religious, and significantly Republican compared to urban, wealthy, etc Portland and Seattle. So, when you look at issues like this is isn't just "a pretty large percentage of the electorate" but rather a geopolitical divide that runs straight down the Cascades.