The thing that differentiates the Seattle situation and the Vancouver situation to me is how the teams performed after leaving.
As a die hard Memphis Grizzlies fan and season ticket holder since day one, I can tell you that before we became the 4/5 seed we are today, we had to suffer over and over through losing seasons, yet we all still supported the team. Don't think that attendance statistics are an indication of the city's support. Memphis is a poor city, and NBA tickets are way out of the average Memphian's budget. Even when we were losing though, the city was always 100% behind the team.
Oklahoma City, on the other hand, was immediately handed a team with Kevin Durant and Russell Westbrook that could contend for a title within three years. Imagine being a Sonics' fan that followed the team for decades, only to see the team return to prominence right after running out of town. That's got to sting.
I always hated it when they showed the ruckus OKC crowd and called it one of the best crowds in pro basketball. That city has not known a losing team yet. Let's make that judgement when they win 20 something games like the Grizz did when they moved into Memphis, in five of their first eight seasons. That kind of losing will build your character as a fan. Hell, we didn't win our first playoff game until we beat the Spurs in 2011.
That's over a decade without a playoff win (and only three appearances)! OKC didn't have to deal with that. Let's see if they still have this great, loud arena when they fall off after Durant's gone.
With that said, I'd love to see Seattle get rewarded another NBA team, especially over cities like Anaheim (although I don't see the owners really approving three teams in the greater LA area).