Taff I had to go back and read your posts to see what you meant by group B people. I think I am pretty similar to you except that you host the big parties and while I have done it, I prefer not to and as I said, I tend to stick to more smaller events and cherry pick, but I do try really hard to mix things up and include everybody at some point.
Some people don't like that, they see it as 'divide and conquer' and can get quite insecure about it, so you do have to be a bit careful about knowing who you can separate and who you can't without it causing a furore. I just prefer to avoid very rigid cliques, mainly because there are too many of us to invite everyone to everything without doing a big party and I don't like doing big parties. I completely agree with you that some people get very set in their clique and can't deviate from it, hence if there are 20 people in the group then all twenty get invited to everything which really limits what you can do and automatically sets the tone of the event. I can't be doing with that nonsense. If you fall on the periphery of a tight night clique then it can be tough, especially knowing those people who don't invite you will happily come to your parties.
I try hard not to do that, and get around to reciprocating with everyone in the end, one way or another.
But most of my Peripheral Friends haven't hosted me either, so I don't need to feel bad about it. We get along fine but they are not natural choices for DH and I to take it to the next level of friendship iyswim. However we do have quite a few mutual friends so we see them quite a bit at other people's events.
If the PBs invited us to a large party then we wouldn't automatically feel obliged to invite them back, although if I went a second or third time I definitely would. Although with one of two of them it would be with slight trepidation on my part as they can be a bit of a handful after a few drinks. They are nice enough when sober they are just a bit too er...excitable for my tastes. But then I would have to 'manage' that by keeping it small and choosing the other guests carefully so that the whole thing didn't get hijacked by excessive drinking and raucousness.
In fact come to think of it they are the reason I don't like big parties. If it's a very late and drunken affair I like to know I can leave when I want to - you can't do that in your own house I know, I've tried 
And sometimes if we don't invite the PFs it's because we really like one half of the couple but really struggle with the other.
But if we repeatedly accepted invitations from them then I absolutely would invite them back, because it would be rude not to. If I didn't feel comfortable doing that then I'd probably not be going to their parties in the first place.
But doesn't tend to happen with the PFs. I think most of us inherently understand where we fit on someone else's social landscape and there is an unwritten code about when you would be expected to be included in things and when you wouldn't.