I agree that both styles presented in the OP seem a little extreme, though I would have a much harder time dealing with the DH's. I certainly don't think 95% of people converse like his family, although IME most are quicker and more prone to interruption than the OP's.
My friend Amy's family talks like DH's--she warned me about it the first time I visited. I take breaks if I get overwhelmed and I don't take it personally if I'm interrupted, although I usually don't push forward with what I was saying. I find I have more success talking to people one on one, or in very small groups, rather than trying to manage at the dinner table, which is more of a circus. They do a lot of, Person A starts a story to Person B, then halfway through Person C starts listening and interrupts with a lot of questions that were covered in the first half of the story, and while A answers them B gets bored and starts a new conversation with Person D, so that when A is telling a new part of the story B jumps back in and has to ask a bunch of catch-up questions, etc.. Crazy! They seem to like it, though.
The thing that would irritate me most, actually, is being told that "almost everyone" converses this way, and I was weird for not preferring it.
Different groups have different styles. In my family the room as a whole tends to be quite noisy, but people are broken up into smaller groups having short conversations (with screaming children providing the background noise). We don't usually talk about anything contentious, like politics; we aren't debaters. We'll usually ask someone how their job is going, for example, and then people who are interested listen to the answer, and people who aren't interested move off.
There seems to be kind of a "conversation circle" within which it would be considered rude to start a different conversation than the one currently going on... Like Anne asks Bob how his job is going, and Bob is answering. Cathy isn't interested in that, she'd rather ask Dave about his garden. But since they're all four sitting at the same smallish table, the volume at which Cathy and Dave would have to speak would be considered to be interrupting Anne and Bob, so Cathy waits until Bob and Anne are done. Or if she really doesn't want to hear about Bob's job, she gets up (meals are usually buffet-style, casual) and goes to another conversation circle for a while.
I don't think we really interrupt much, but if someone seems to be trailing off, someone else might jump in; we don't have many awkward pauses, we'd rather fill them with something. We would have to make a conscious effort to accommodate someone who needed significant time to think before replying--it might happen with a shy child, someone whose first language wasn't English, etc.. Or if we knew someone just needed that extra bit of time we would try to remember that, because we don't want people to feel left out.