GPLv2 is silent on the subject of trademarks, and is a bit vague about additional restrictions -- section 4 would apply to trying to restrict usage of the code, but trademarks are a separate thing. GPLv3 explicitly allows you to decline to license your trademarks (see section 7, the paragraph starting "Notwithstanding any other provision of this License", clause e). This isn't generally called out as one of the big differences between v2 and v3, so I think it's intended more as a legally-spelled-out clarification than a change.
I'm not a lawyer, but the GPLv3 in particular seems compatible with the idea that you can tell someone that they can only use your trademarks so long as they behave in a certain way... so long as you're still allowed to fork the code, strip out those trademarks, and continue using it. Which does seem to be Matt's position. (I mean, he also wants to restrict access to Wordpress.org services, but that's even less in the GPL's area.)