That's just silly talk. Red Hat doesn't control these other repositories so there is no way Red Hat could be expected to speak for those organizations if Red Hat were to agree to cross-distro version locking.
Canonical most definitely control PPAs as they are part of the Launchpad service running on Canonical funded infrastructure. Canonical could turn off the Ubuntu specific PPAs tomorrow. And of course there are the Canonical's OEM specific partner repositories for Ubuntu pre-installs.
I just want it to be clear as to what Canonical is actually willing to agree to from their end as to how far version locking will go and how big an impact that will have on end-user.
Canonical could easily agree to some sort of cross-distro version locking on core components in main and then break the spirit of that agreement by making use of the PPA infrastructure they control and encouraging users to pull enhanced versions of core components from PPAs or OEM partner repositories they directly control.
But you are right, they don't need to use PPAs to break the spirit of any cross-distro version locking agreement. They could also ship multiple versions of core components in Ubuntu proper like they are planning on doing with the kernel in order to get Android emulation support out to people in Karmic. Would shipping an optional 2.6.29 kernel with Android enhancements be considered a breach of a cross-distro version-locking agreement if everyone agreed to shipping a 2.6.31 version?