The thinking seems to be that Microsoft and Apple both rely on CC code and therefore would be compelled to defend against people being able to pull their code from CC and then force MS or A to license the code or replace it.I don't disagree; I just remember that we all said the same thing about the OGL.
The more salient point is that the idea that the 5.1 SRD is in any way safer under the Creative Commons is largely paper thin, and seems to be based more on a belief (that Apple and Microsoft will somehow step in and stare WotC down, apparently) than on any sort of solid legal foundation.
I did a quick search but have not found any confirmation of that, though. I would be interested if anyone has an article that explains the situation.