I know in many areas offering to bring a dish to a dinner party is frowned upon. However, in my social and family group, we often have less formal dinner parties with invites issued with "Hey, ya'll want to come to dinner on Friday" and a response of "Sure, what can I bring?" is almost standard (formal parties you don't do it).
This is how it is in my circle, too. The answer is either "how about a salad? [or whatever]" or "Nothing, we're all set."
I think that the hosts in the Miss Manners column were being a little too specific, especially as they didn't specify what dessert they wanted right away but waited until the letter writer planned something else. (I do think she was being really childish to not want to go at all or to bring something they'd hate.) But Miss Manners is right that if you make an open-ended offer of "what can we bring?" you may be stuck with an answer you don't like. Better either not to offer at all or to offer to bring something that you do want to bring (or a choice of a few things) and let them say thanks or no thanks. That's what I usually do.
Suppose the hosts, immediately upon being asked "What can we bring?" replied, "Well, we were planning on a pineapple cheesecake from Yummy Bakery. Would you like to bring that?" It seems to me that the guests could then either agree to do that or respond with "Oh, if you want us to bring dessert, I'd love to make a XYZ Torte. Would that go with your menu?" And the host could then either agree or say, "No, we definitely want that cheesecake. So how about a salad instead?" or whatever.
I mean, presumably these people are friends and not first-time guests -- otherwise the guest might not have offered to bring something, and the hosts very likely would have declined the offer to contribute to the meal. So to me it seems obvious that simple communication between friends ought to resolve this. If it were close friends, I might even say, "Sure, but can I get a different flavor instead of pineapple? I really don't like it." Especially if we were to be the only guests. After all, hosts are disappointed if their guests don't like the food, so they would probably be glad for the heads-up that you won't like it. If they are close enough to ask you to buy a pineapple cheesecake, then they are close enough to hear that you hate that flavor!
I have to wonder how much the LW's dislike of pineapple enters into her irritation, too. But it brings up an interesting question. Suppose you were the guest, and you don't mind being asked to buy or make a dish, but it's one you dislike? What should you do? Sounds like a good time to offer to make something here didn't look good or something! But I wouldn't. I think I'd just get what they asked for and eat only a little bit, the same as if it were served and I hadn't known anything about it. (At some level, I'd actually be glad
I didn't like it, because then it's easy to resist ingesting those calories!)