I noticed in the gamedev faq it says:
If you have questions relating to ...
- subject 1
- subject 2
and it is not about...
That sounds like a typo to me.
I think it is correct; I read that section as a list of topics that are permissible (game design, for example) followed by a list of question types that are not. It says, if you consider one particular combination of both lists, "if your question is about game design and is not about how to get started in game design, then your question is acceptable."
That isn't to say we couldn't reword it to be more clear, however.
EDIT: Oh, I see I think, you were talking about the plurality/singularity agreement and not the "and" at all. Nevermind!