I don’t understand how AGPL allows Canonical to make and sell proprietary copies of this software without violating their license. That’s the only way your scenario could happen.
“To release a nonfree program is always ethically tainted, but legally there is no obstacle to your doing this. If you are the copyright holder for the code, you can release it under various different non-exclusive licenses at various times. […] the GPL is a license from the developer for others to use, distribute and change the program. The developer itself is not bound by it, so no matter what the developer does, this is not a “violation” of the GPL.”