To be fair I don't think friendlies were ever about fans, they were about getting the team ready for the season. It is easier to do this locally, but when there's monetary benefit to be had by going far afield, why not.
And to the North Americans here, they might do more than one game. Chelsea played a friendly in Chicago in 2006, and in 2005 played a friendly in Massachusetts and another in Washington DC. So when they play in the US, they do play both coasts! And this won't be the first time the team has played in Seattle, in 2004 we had friendlies in Seattle, Pittsburgh and Philadelphia (two more eastern cities).