There are two, and only two, copyrights on any song:
1) The melody set against a chord progression.
2) The lyrics
When an individual writes a song, he owns the copyright for both of these. If he enters into a music contract with a company, he might have to give up one, both, or parts of one or both, as defined by the contract.
The copyrights for these pieces of music come into play when:
1) Someone else records the music.
2) The music is played on the radio.
3) The music is used in a film, or some other kind of score.
In Canada, we have an organization called the Canadian Musical Reproduction Rights Agency, a non-profit group that basically has a huge database of songs for recording artists to look through in order to find out who they have to pay royalties to (I know there's something similar in the states, but I can't remember what it's called).
Every time a song is recorded, with the intention of selling it for profit, the recording artist has to pay 8.5 cents for it, if it's between 1 second and 5 minutes long. For each additional minute, you get to tack on another 1.7 cents. This covers both the melody and the lyrics.
There are similar guidelines for radio and film, but they elude me at the moment.
As you can see, the copyrights for lyrics apply only in a case where someone is reproducing them in a piece of music (or sometimes in a songbook). By selling songs that have lyrics, Apple has already covered themselves legally to distribute the lyrics (you can't split a lyric away from a song...that would be ludicrous) under whatever deals they've made with the various record companies and individual recording artists.
However, some of the older lyrics, like the early jazz recordings, soon won't have any kind of restriction on them whatsoever. 50 years after the death of the author of a piece of music, it becomes public domain, and anyone can record and distribute versions of the music with no charge. This is only just starting to happen with popular music, because most of the composers are either still kicking, or it hasn't been 50 years since their death. So you can imagine how pissed off MJ is going to be when the 50th anniversary of John Lennon's death rolls around.