The "it" in "it is not free" here
means the right to distribute
something (also commercially), and if this costs something, "it" is
not free in the RMS sense.
Actually, if you look at:
http://www.gnu.org/gnu/initial-announcement.html
you'll see that originally, there was no distinction made between the
two English meanings of 'free'. That came later.
I think it's unrealistic to expect that if you want to distribute
something commercially, then you should have a right not to pay for
it. It breaks the virtuous circle that makes free software great.
I think an important distinction between music and software is that
software requires active developer input to retain its commercial
value, and the equivalent isn't true of music. For example, plenty of
1950's music still has commercial value, but most 1950's software
does not.
Given the often short careers of musicians, there must be plenty of
people who are still getting an income from those old hits. (Probably
not the musicians who made them, but that's another story - just ask
the Rolling Stones). Without a 'pension' in the form of retained
commercial rights, what would those people do? Be forced to keep
playing live until they look like a bunch of ridiculous old men
prancing around on stage? You've got to feel sorry for them - I'm
sure they'd rather be playing golf or something.
Cheers
Daniel