I've been in Seattle the last 5 years, 3 of those in new "luxury" buildings. No apartment building I've lived in or toured has AC in-unit, though newer buildings will have it in common areas only. Further, many places have leases that disallow window-mounted AC units (not that the awning windows would cooperate). It's rough, esp. with windows on only one side for most apartments.

I'd imagine developer incentives + LEED certifications are going to maintain the status quo.

Only in luxury or eco buildings. Most of the places I looked at in downtown Bellevue last year either lacked AC, or lacked windows you could open and had very centralized AC (the green buildings).

My current place has a ceiling fan because it is on the top floor. It can get really hot up here, but still no AC unless you buy it yourself. It was built in the early 00s. Even the fairly newish building (< 10 years old) we looked at next to City Center lacked AC.

I think it's mostly a function of building age. A lot of Seattle housing stock dates to 1920-1940. Apartments tend to be newer; certainly the new large apartment buildings all have it (as well as modern spec insulation).