Refusing to allow the showing of something positive about McCain fits quite well with Hollywood's m.o. It is simply the flip-side of the coin that allows Lions Gate Entertainment to release W this friday or Fahrenheit 9/11 in 2004. If the project paints a Republican in a bad light, by all means, release it before an election. On the other hand, if it shines a positive light on a Republican, well, we wouldn't want to affect the election.
As Lionel Chetwynd put it, "finding someone in Hollywood who says they don't want to affect the election is like finding a virgin in a brothel." Take both claims with a grain (or ton) of salt.