The strangeness of Seattle and of Washington State west of the Cascades doesn't come from progressive values or from people doing things that are in themselves necessarily strange. Instead, it comes from a generalized feeling of difference, of being in a place where everyday life exists in a familiar but slightly different form, one whose methods are recognizable, and navigable, but still off enough to have to be relearned.
Seattle and Washington, taking that to mean western Washington for the moment, constantly defy attempts at stereotypes. Coffee, Pike Place Market, ecological values, and the heritage of grunge rock, are all there, but they don't define it anymore than a glossy travel magazine's one off would. Stereotyping Oregon is easy, especially Portland. When you go there you can recognize the city as possessing magnified tendencies that are found elsewhere in the country, and "Portlandia" trades on it. Instead of organic chicken farms run by gurus, Seattle's uniqueness comes from businesses that reinvent the types that they come from, in ways that are often not spectacularly weird, but second takes on familiarity.
Settled very late, Washington still plays catch up to the rest of the country. Western Washington is cut off from its eastern neighbors, both in state and out, by a forbidding mountain range on one side, and north enough that it's beyond the direct influence of California culture that Oregon experiences. With no obvious model to go from beyond membership in a generic United States culture, it's still constructing the cultural and physical infrastructure that other states have absorbed naturally from their neighbors. It's still an unfinished work that's being created as we speak, and resembles a related country in formation.