I would have been a bit pissed off too if all your friends had been invited. If it was only a couple of couples, then that is a different thing. They dont have to invite you to everything, but if it was a group thing it seems a bit naff. You could just say, your party looked good from what i saw on facebook hope you had fun, so they know, you know.
Perhaps they didnt want you to feel awkward i it was a couples thing rather than thinking youd be after their husbands? The thing is, when my dh and i go to a party, which is a rare thing, we dont even spend the evening with each other, we are so busy catching up with everyone else, so its not like youd be a billy no mates. . . Unless it was one of those keys in the bowl type of parties?!?
Also, i know what you mean about inviting you to the jamies thing. I have a neighbour like that, whenever they want some support for a virgin vie, jamies, phoenix cards they invite me over, but when they go out to the local pub quiz every week, there is no invite. Perhaps. Just look a but thick?!?
Or you could go for the blunt and sarcastic, 'thanks for the invite to your party!' Heehee.