Well, I am to blame in our marriage for the exact same behavior you describe. It is my husband who wants to talk to me all the time.
So unless he has my complete, undivided attention, meaning no computer, no laundry, no dishes, no cooking, no reading, no music, I do not hear half of what comes out of his mouth. He must tell me before he speaks that he needs my attention, OR he must assume that I am truly not in a listening mode. I am constantly thinking about things...so someone starting up a conversation with me at home is a bit of an intrusion, as I already have one going on in my head.
Then the same consequences of what you describe above....I started to pretend to understand what he said, and put together a reasonable half-hearted answer. Oh, did not go over well.
Turns out, after years of him being frustrated with my inattentiveness, and some therapeutic intervention, I have ADD...I was shocked. I hate to admit it, but my ADD meds have made me a much better listener, I'm less irritable with him wanting to talk as I can focus longer now.
However, with that said, I still will not sit and talk about meaningless topics, like Suz T does below. I will talk to him about work related issues as long as necessary, but I have no tolerance for electronics and computer conversations.
Also, I've heard many husbands complain over the years about how their wives talk on and on about other people, and little family conflicts. I do not bore my husband ever with any day to day neighborhood or school happenings or gossip. It's got to be really big or has to impact him directly for me to discuss other people with him.