It looks like you can DVDs in bulk for between 20c and 10c per disc. If you're really serious about protecting your airgapped computer, this is a very reasonable price to pay.
Sure, so is using a rewriteable DVD, but neither is much more secure than formatting thumb drives before mounting them. Convenience is the only argument, and it is not all that hard to set things up so that you always format thumb drives that are plugged in.
A thumb drive is, or can be, a tiny computer that can lie about its contents depending on what's asking. I don't see a particular exploit in Schneier's case, but a thumb drive could be made that behaved differently depending on whether a Mac or Windows PC was trying to talk to it.
APT in a flash drive is just a cute trick. Just because you wrote zeros over it doesn't mean that the APT thumb drive firmware won't give you a trojan next time you read a the right kind of file off of it.
Or maybe it waits a week before it starts injecting binary, just to wait out your test and validation procedures...