Well, you seem to be talking about people showing a lack of consideration rather than implying you are stupid. They either can't be arsed, or don't think their inane comment is worthy of repeating.
It is rude and inconsiderate of them, especially if you have actually asked them to repeat something. But, it does take a bit of practice to get used to facing a deaf person and ensuring they are included in a conversation, especially when it's amongst a number of people.
I have a deaf friend who lip reads and find talking to him one to one quite easy, though I've learnt to structure my sentences differently, always starting with the subject; 'this thing...something about it' not 'something about...this thing'.
In group conversation though, even amongst friends who are generally considerate, some are more or less competent about facing him, avoiding distracting little sub-conversations he can't see and checking that he's following, which does often mean repeating some things. Sometimes one friend takes a lead on that and effectively translates, 'so and so just said...' while we all pause. If she does this with what the speaker considered a very incidental remark, they can feel a bit silly, so I think we all try to keep to the important points more and keep the conversation slower. Sometimes, when a conversation is fluid, faster and no-one is taking that role, he does get left behind until someone engages him one to one.
So, I'm saying yes, people are often useless, mostly because they lack confidence about how to speak to you (or forget when they're drinking) but if you tell them what you want and they refuse to do it, they are being rude, albeit possibly through poor social skills that afflict them more generally but, rude.