And again, Canonical is not "offering the service of building/storing binaries" - if they were, Mint could simply use any of the mirrors and simply blacklist Canonical's own server, and the only way Canonical could prevent this would be to demand the same terms from all the mirrors, which would pretty much be shooting themselves in the foot, since Ubuntu would not be able to function without all the free, mirrors which they don't pay for and which help distribute their packages for them.
Canonical is instead attempting to argue that Mint needs to sign a license for the binaries themselves, this is IIRC mentioned in the Distrowatch article. Clem even states there that he doesn't consider Canonical's claim valid, but is willing to play along in order to maintain the peace. Which is, ok, his decision to make but I don't agree that it's a good course of action in the long term. If Ubuntu shuts down because of GPL violations, then Mint will have to rebase on something else, because there'll be no more Ubuntu.