Also, I think most folks doing the Pacific Coast Route want a more direct routing, and going the "long" way around the north and west sides of the Olympic Peninsula can add almost a week to the trip. It's faster to stay "inside" and follow the Puget Sound south towards Olympia and turn out to the coast there.
And the Washington coast is a lot different than either the Oregon or California coasts. In OR/CA, 101 or 1 stays fairly close to the ocean and beaches are pretty accessible. In Washington it winds its way many miles inland in many spots, esp. on the Olympic Peninsula. In SW Washington, there are numerous bays and inlets that US 101 winds around, so you'll see "water" but it's not the ocean. The one benefit to 101 in Washington is that it's quieter than 101 in OR and CA.
I biked around the Olympic Peninsula in 2010. It was a nice tour, but as I said above, 101 stays pretty far inland for most of the way from Port Angeles to Aberdeen. There is only one section that hugs the Pacific Coast, and that's only about 10 miles long. Also, while Olympic National Park is nearby, 101 only passes through it in a few spots, up around Lake Crescent (which ironically enough features the worst riding on 101) and that section on the coast at Kalaloch. If you wanted to access other areas of the park, like the beach at Mora or the Hoh rain forest, you'll need to be doing 20 to 40 mile round-trip detours to access these areas of the park. Most of the ride consists of looking at trees and hills and clearcuts, which isn't bad, but you're neither going to be riding directly through the Olympic rainforests nor seeing the Pacific from the saddle for the most part.
I'd like to go around the Olympic peninsula again at some point, but I know that in order to do more stuff in the park, I'll need to plan more time.