The issue of 30-40 year old songs being downloaded without permission is just a ruse being used by people who want music for free anyway. The vast majority of music being illegally downloaded are songs that are only a few years old at best. There is, as you have said, room for debate over how long copyrights should be extended. That debate really has no bearing on most of the music being downloaded. Even if the copyright was put at 10-15 years, most downloads would still be illegal, and rightly so. So people just can't handle the fact that they will have to pay for something.
Good point. I am sure the most downloaded songs are Eminem, Green Day, Jack Johnson, or whatever the flavor of the month is.