I sent an email out to the above address a couple of days ago, asking how to go about receiving the replacement discs. I didn't attach a receipt at all; my mailing address happened to be added to the message as part of my signature, though.
I received a reply today saying that they were out of stock, would be receiving more next week, and would then ship the replacements to me ASAP. Apparently you don't have to send in the defective ones, or even show proof of purchase.
We'll see what happens in a week or so.
Matches my experience as well. The email said they should be shipped very soon.