The emissions testing is just a nice little bonus for the state as well..... here is a 'cut & paste' from the link I posted above:
In addition to making sure all citizens are taxed fairly, the State patrol has testified that using a primary Washington residence address on vehicle records will enhance their ability to preserve the safety of the public and to quickly notify accident victims' relatives. It also will help make sure that vehicles subject to Department of Ecology emission tests will receive appropriate notice.
This is why I live in Kitsap County. Less Tax, Lower cost of living, Less Crime (except if your name is RYAN, and you drive an EXPLORER) and NO emission testing.
Ryan