The Penguins bought out the contracts of Sebastian Caron and Shane Endicott for 1/3 of the value of the contract, per the NHL rules. Thibault could have been bought out as well (or instead of Caron), but it would have cost the team 2/3 of his $1.5 million salary for next year, or $1 million.
I'm disappointed to see them cut Endicott, since guys with size like his are hard to come by (though they just drafted a player with his size in Jordan Staal). The team is really solid at the center position, though, so I guess it's not that big of a loss.
Caron has proven that he is a capable backup in the NHL. I think he'll catch on somewhere. This could open the door to Sabourin to be the backup if Thibault doesn't return from his injury as expected, or repeats the performance of last year.