>> There's a communal, shared, DIY philosophy behind it; it's art by and for regular people (folk art), to be shared;
Yes, I agree. I guess I dont see the conflict. If you play any of these songs, change a few verses, some melody and some chords, then you can claim the copyright just like Bob Dylan did. That is what I think he is trying to get at in that speech.
Notice how is says the following in his copyright claim:
"Basis of Claim: New Matter: rev. melody & new music." [1]
There are many artists that have copyright claims for the same essential song title. Search for Walking Blues, John Hardy or any old fiddle tune like Shady Grove, Blackberry blossom, man of constant sorrow etc. There are a ton of these songs out there where anybody can make their own mark and claim the copyright because literally everybody does it.
Try doing that with 'Times are a changin' and I can guarantee you its not the same unspoken code because its not one of those tunes that have been passed down by generations of musicians and told and retold. The bar will likely be much higher for you to claim your artistic expression on that copyright.
That was the point I was trying to make here. I mainly objected to your 'Can I sample one without his permission?' since I don't think its the same thing.
[1] http://cocatalog.loc.gov/cgi-bin/Pwebrecon.cgi?v1=14&ti=1,14...