I find myself to be much the opposite. I have trouble focusing on on any one conversation, I'm too easily distracted. I can't hold a phone call or conversation while a TV is playing at similar volume. In a restaurant, I feel like I hear all conversations and the music, and I can't seem to shut them out. It's not that I'm listening to all the conversations, but I hear them, and it makes focusing on the conversation I'm trying to hold difficult.

With programming and reading, however, I do find that I can shut out background noise, and I suspect this is because it's a different kind of thinking than what distractions around would be causing.

I suspect that because the attention is given to a mode of thought (reading, programming), and that that mode is not competing with other forms of the same mode (I'm not trying to read two books simultaneously), that this enables someone (or maybe just me, I dunno) to shut off the other senses. While with listening and hearing multiple conversations, it's like trying to read and having random words getting thrown into the sentences you're reading.