I don't think the tbirds play in key. I believe they at in kent.
You're right. I wikipiediad it. Looks like they moved in 2009.
The Thunderbirds originally played in the Mercer Arena before moving to the Seattle Center Coliseum (later renamed the KeyArena). Unfortunately, the KeyArena was ill-suited for hockey, as the sight lines were designed for basketball and the ice surface was so far off center that the scoreboard hung over the Thunderbirds' offensive zone instead of center ice. In 2009, the team moved from the KeyArena in Seattle to the newly built ShoWare Center, 20 miles south in Kent, Washington, where they became the anchor tenant. 
I don't agree about Seattle being a sports town, the majority of the people in the area are apathetic towards sports. The city refuses to contribute any money towards venues at all, they want everything 100% privately funded. I'm pretty sure there is a law that the county/city cannot support any sports franchise unless they are profitable. This all comes from the voters. I don't think that's without merit, but it shows that money is more important to the populace than having a team.
They refused to help fix key arena, even though they knew they could lose their basketball team. The sonics couldn't have been that important to them. Then there is the Mariners. No one goes to see the Mariners anymore, despite having a gem of a stadium. They have one of the worst season ticket bases in the league, attendance is utter crap for a MLB team. They went from very high attendance 10 years ago to a bottom feeder. The sounders are doing great, but they are shiny and new, just like Phoenix once was. Only time will tell if they sustain that. The only team that has proven it can succeed there is the Seahawks, because let's face it, the NFL is wildly popular everywhere.
This post is very mis-informed. I've lived here the last decade and it's a very good sports market. The Sounders are one of the top draws in MLS. The city never got a real chance at addressing the arena issue before Clay Bennett came along and stole the team (with Commisioner Stern in his back pocket). Do some research on it and you'll learn it didn't go down the way you're representing it.
Also, the Seattle metro area has a huge hockey fanbase. We have the 5th or 6th largest adult rec hockey league in the country. I play year round for a couple teams and there are plenty of hockey fans here with money to burn.
An arena is not going to be an issue and the Key, while not being pretty would be an acceptable, temporary and home (2-3 years to build new multi-purpose arena).
Key Arena would seat 15,177 for ice hockey and is 52 years old. Estimates that any NHL team that moves there would lose 20 million a year until the new arena is finished. Key Arena only provides 9000 unobstructed seats when configured for hockey. Sound like something the NHL would want to get into for 2 years?