Good and essential point. If the copyright holders and courts would recognize that argument and spend their millions on setting up ways to correctly rename "mislabeled" files, we'd quickly see infringing content clearly identified.

p2p users should not be held responsible for the ripping software that mislabels files, or commercial distributors who fail to label their files appropriate with new electronic standards.

I would gladly filter all searches to block © files, or only use them knowing they were to be paid for or deleted. You're right--if the copyright holders leave their goods on the street, they had better be clearly marked.