If you want to get a little more depressed about music changes to TV-on-DVD releases, Sitcoms Online has a list of the music changes in season 2 of Happy Days.
Not only has Paramount replaced "Rock Around the Clock," they've cut just about every real '50s song except Fats Domino's "Blueberry Hill." (If you don't license "Blueberry Hill," releasing Happy Days is pretty much impossible, given that it was sung about 9,000 trillion zillion billion times in the series.)
The one thing I'll say for Paramount is that they did license all the music for the first season of Happy Days. Then the set didn't sell much, and they lost money on it. So they can at least point to actual proof that season 2 of Happy Days wouldn't sell enough to make back the expense of paying for the music. Obviously this doesn't apply to a studio releasing the first season of a show with all the music gone (but we've been over that before).