I think Canonical is just creating unnecessary problems for themselves with no gain whatsoever. And tactics like this could very well be the reason why Valve is now distancing itself from Ubuntu...
From the GPLv2
"... The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language..."
Translating into binary form via a comipler, is quite clearly a derivative work, still refered to therin as the program.
"Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein ..."
So while you aren't required to distribute the binary, niether can you place restriction on people who you distribute it too beyond those of the GPL.
When canonical talks binaries, one assumes they mean DPKGs. I cannot say if it is legal to restrict their use or not. That they are containers for GPL software may or may not be relevant.
Furthermore Vim is 100% right with regards to restricting repositories. Those are THEIR servers. They can restrict them all they want. An analogy: if you kept a stock of CDs with GPL software on them in a shed and let people come and go as they please to take a CD, but only if they agreed to stay for a cup of tea too, would that be GPL violation? No. To suggest so is patently absurd.
Sigh... I'll say this one more time. Placing restrictions on the use of repositories would be within Canonical's rights. If Canonical wanted to say "Mint, you guys may not use our repositories", that would be legal. What they cannot do is tell Mint "you have to sign this license in order to be allowed to use binaries compiled by us even if you get them elsewhere". That is very clearly against the GPL.Furthermore Vim is 100% right with regards to restricting repositories. Those are THEIR servers. They can restrict them all they want. An analogy: if you kept a stock of CDs with GPL software on them in a shed and let people come and go as they please to take a CD, but only if they agreed to stay for a cup of tea too, would that be GPL violation? No. To suggest so is patently absurd.
They can place restrictions or conditions on the usage of their repositories. HOWEVER, those conditions cannot contradict the GPL license, because Canonical has themselves a prior agreement they have to abide by - the GPL license. When Canonical uses GPL software themselves, they have agreed to abide by the GPL license, therefore, placing restrictions on the usage of their repositories which effectively causes restrictions on how the recipients of those binaries are allowed to use them - is against the GPL.
I think there was even a section about this in GPL, I'll look into it later.
Being DPKS doesn't change the least. In fact, DPKGs are a derivative work, as their value is only on their contents, which are in several (but not all) cases, GPL. It's just the distribution media: the very same way you can not restrict redistribution of a CD containing only free software, you can not restrict redistribution of a DPKG containing only free software.
They contain three parts wrapped in a single ar file.
--version info (of the .deb format, not for the package)
--a psuedoroot directory containing all the files to be copied into the filesystem. (clearly a derived work in itself, except perhaps added disto-specific init or .conf files)
--a control directory containing Scripts to run pre, post install, checksums for all of the files in the above data directory, and a controll file listing dependencies and containing package information.
Don't believe me, go and pull one apart.
Those scripts could come under separate copyright if they were distributed repeatedly, but going back to section 2 of the GPLv2 " If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it."
Leading me to conclude that because the wrapped it up together in a single file the licence on those files must be compatible with the GPL. Besides being in a single file, it's also designed to all be pulled with a single command.
To actually control the copyright-able parts they add in they might be able to do something like gentoo's portage system does. All of the install information, checksums, pre and post install processes, distro-specific init and .conf files are kept in their own sub directory, and are mixed together only when the user initiates the install procedure. However this still wouldn't give canonical much leverage as they are distributing both together as a distribution. They would have to go a few steps further and make the download of the sub-directory a user-initiated process during installation. Of course this would backfire on canonical practically, because many third parties would be willing to step in to provide third-party directories.