That could be the reason but CBS also has this little umm tick if you will, I remember when a show "Touched by an angel" was on, they locked in the cast for another season or so. Then they decided the show went as far as it could and decided to cancel it. BUT one would think the actors are free, guess what, that wasn't so, they were still locked into CBS, meaning if they wanted to guest on another network they had to get permission, if they wanted to do a movie for another studio needed permission. Fineally after the threat by the cast of a joint lawsuit they came to an agreement that after six months their contract would be null and void due to the ending of the show, but maintained if they do a movie in the future.
This became a real public arguement at the time, I am sure many celebs at that point went into negotations with this in mind and a loophole out of it. Be it canceled show, killed off character, etc. Course LF may have only signed for that length because of the fact that its the tenth season, one can never know for sure how long it will last at this point they tend to take signings in the smallest amounts.
