Wow. This is stupid as hell.
Saying that the artists and songwriters loose out on this is just a flat-out lie. I don't see anyway this could possibly hurt them, unless of course they have sheet music out (but more than often, bands that have that already have more than enough money. And even so, what does that take away from them? A whole 0.4% of their profits?)
Think about it like this:
You learn a Nevermore song from a tab site, play it for a friend, they like it and now have an interest in the band. So they download some songs and pick up an album or two.
Plus the fact that not one band has spoken about this.