A common criticism of the MS OOXML specification is that the patent promise is insufficient to allow an open source implementation without problems, and this story makes a specific claim about the patent license that we can examine:
"What Microsoft intends to do with its OSP is to forbid sublicensability, which is one of the cornerstone for distributing GPL code."
Legally, there are really two aspects to this: first, is sublicensing a corner stone for distributing GPL code (covered by copyrights), and second, does that apply to patent rights (rather than copyrights)? It's important to address both those aspects, since either could be true and would affect distribution in different ways.
First, the copyrights themselves. The GPLv2 doesn't address copyright sublicenses explicitly, but does say that "the recipient automatically receives a license from the original licensor" (section 6) which isn't a sublicense. GPLv3 is explicit, though: "Sublicensing is not allowed; section 10 makes it unnecessary." (section 2, last para).
Now addressing patents, the position GPLv2 takes on patent licenses is "a patent license [must] permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you" (my edit, the GPL states that in the inverse, section 7). It doesn't require the ability to sublicense, or request it.
GPLv3's section 11 (Patents) is considerably more complex than the v2 counterpart, but in essence requires contributors to grant a "non-exclusive, worldwide, royalty-free patent license". It doesn't ask for the ability to sublicense, and it's difficult to see why you'd need one given the initial license granted by contributors.
