Song Credits in Movies

Why is it, that in a motion picture, if only even a few bars of a song is hummed, credit is given at the end of the movie; but in an episode of a tv series, no song credits are given?

WAG:
[ul]
[li]TV time is expensive, so it is sold to sponsors. The more time for commercials or their equivalent, the better. So music credits, besides original music composers, aren’t included. As long as the producer of the show pays ASCAP for any songs played, they’re generally happy.[/li]
I suppose an artist may insist on some sort of recognition in lieu of or in addition to their ASCAP royalty. I noticed that on “Ally McBeal”, Vonda Shepard is listed as a cast member rather than listing her songs in the credits. This probably gets her more exposure.

The acting cast is of course in the credits; it’s in their contract. (Besides being 1st or 2nd in the cast credits, last is a coveted spot.)

Often a credit like “Mr. Smith’s suits provided by Botany 500” appears. This is basically a cheap commercial.

[li]For movies, often all the songs (in their entirety) are put together on a soundtrack CD. The songs are then listed in the credits so that people who want to buy the soundtrack CD can see what they’ll get. The production company gets a share of the CD sales, as well as the various artists.[/li][/ul]