I don't know if the deal Apple cut with CDBaby is responsible for this, but nearly eight months after I bought Supermodifed from Amazon, it's available on the iTunes Music Store, along with several other Amon Tobin albums. They've also added Death Cab for Cutie and Dntel, though these might be more of a followup on the inclusion of The Postal Service, which is a side-work band for the leaders of Death Cab and Dntel.
Anyway, I'll be trying a few more probes to see how large my miss rate is now. Used to be 70-80%, without even trying. Now? I'll let you know.