I have to say for the people quoting her that don't think Miss Manners is the best authority on this particular wedding because she's American. You are referring to Judith Martin right? Well she's American and this is, not only a British wedding, but a British royal wedding!
A royal wedding has it's own set of rules and traditions. Not to mention it's complicated by security and space concerns.
I agree that there are some people who they are expected to invite to the ceremony because it is a state affair, and the reception is a private event. As for why the queen didn't go to the reception. Who knows? Too tired for such a full day, her presence automatically makes it a state affair, again security concerns, family feud with Prince Charles. All are possible.
Her name on the invitations. I'm half-British (dual citizen) though I grew up in the US so I'm not incredibly familiar with the details of royal tradition. However, I believe that this is because she's the Queen and not so much about being the groom's grandmother. Sort of an indication that the royal family approves of the marriage?
Don't quote me on that, but that would be my instinct based on my somewhat limited knowledge of my other culture.