If the Kubuntu marks were in fact under the stewardship of a non-profit I would agree wholeheartedly with your statement concerning the nature of coopetition with regard to multiple vendor support for an upstream project.
Projects under the stewardship of the Apache Foundation for example... can have multiple vendor support.
However... since the Kubuntu marks are controlled by Canonical still..and the public trademark policy Canonical provides specifically prohibits use of the marks for anything with commercial intent...then no..this isn't really a parallel situation for things like all the ASF projects.
It's more of a parallel of Openstack. Openstack is essentially dominated by Rackspace and Rackspace owns the marks (well actually Openstack LLC ownes the marks but Openstack LLC is a subsidiary of Rackspace....). But Rackspace has already publicly stated their intention to create a non-profit foundation in 2012 and transfer ownership of the marks. Vendor-nuetral control of the branding does matter to foster to prevent inherent conflict of interests in a multi-vendor support approach to a project.
What I am saying is Kubuntu would benefit from a similar vendor-neutral approach to the marks. Blue Systems doesn't need to own the marks...nor does Canonical. They just need equal access for commercial use. A vendor-neutral steward of the marks would provide that.