First, the major sites that got busted were ed2k, not BT. The only major BT site to go down (Phoenix) went down voluntarily because they didn't want to risk any trouble. If SuprNova is still alive, you know that BT is a long way from dying. (edit: nevermind, just noticed that they closed down today, but it seems unrelated to the crackdown; they've had technical difficulties for quite some time now)
Also, as another poster said, there is a lot of legit BT traffic, too (like the release of FireFox).