getting something for free - costs Amazon money
People that go to Amazon to get these things like album art (for music they already own) are basically stealing bandwidth from Amazon. While information was meant to be free, a company like Amazon probably pays a steep bill for bandwidth.
Amazon probably left the system wide open in hopes that people would dream up some novel new uses for the data that would also drive sales. But now if Joe Blow uses an application that invisibly gets the good stuff from Amazon, then Amazon is subsidising the application via its datacenter, and also getting no recognition for it (and also no sales to offset it.)
I won't go so far as to say "ha-ha freetards/leeches", but I probably could.