A goalie can be the difference between losing in the first round and being a Cup champion, and it sure as hell was here. Let's not forget, Boston won two Game 7's prior to the Finals, and against two really good goalies to boot. Thomas outplayed Carey Price in Game 7 of round 1 (Bruins won in OT), then outplayed Dwayne Roloson in the conference finals (Bruins won 1-0).
As a Wings fan, I have seen many, many instances in the playoffs where I thought we were the better team, but their goalie stood on his head and the opponent was opportunistic in their chances to score. Examples include JS Giguere carrying the Anaheim Mighty Ducks from a 7th seed all the way to Game 7 of the Stanley Cup Finals in 2003, Miikka Kiprusoff doing the same thing for the Calgary Flames in 2004, and Dwayne Roloson accomplishing this same feat in 2006, when the Edmonton Oilers were the EIGHTH seed. Your goalie really can steal more than a game for you in the playoffs.
This is what happened in the finals. Hell, Boston almost stole one or both of the first two games in Vancouver. But they kept grinding away and finally got Luongo and the Canucks to crack. Full credit to them. It was a pretty big upset in my eyes.