Sibir offered more money (after tax at least) and 2 years instead of 1. The Olympics might have also played a factor, but he is on record talking about the importance of earning as much as he can.
He is about average. His initial foot speed is quite poor and I think people just draw too many conclusions from that.
A little late with my reply to this but he hasn't ruled out playing in the NHL completely. He's obviously not interested in playing in the AHL anymore at his age and what could make in the KHL. I think he was also concerned about the depth at center with Blues, he needs to center the second or 3rd line if you want to get the best out of him and I guess he wasn't sure he could get those. He is in good relations with Sibir so if the right opportunity should present itself from NHL, he could get out of that contract without too much of a problem (buys out the second year with his NHL signing bonus or something like that).
When it comes to his skating, while I haven't seen him play recently except for some Euro Hockey Tour events and the Olympics, he has worked hard on it in recent years and is at least average or slightly above with it these days.
Also as I and several other Finn posted on the main board GDT, he's quite the character in interviews and the NA media would either love him or hate him. The comment during the intermission on Finnish tv about Kane's missed penalty shots ("if you don't have the hands, you won't score") says all about him.