Gamasutra - Ode to Short Dialogue
Big Huge Games' Ben Schneider (formerly Iron Lore) has written Ode to Short Dialogue for Gamasutra. Before you grab a pitchfork to protest dumbing down games, Ben is primarily writing about short sound-bites, such as ambient background comments, and makes some good observations. On BioShock and Assassin's Creed vs Oblivion and Mass Effect:
Compare the overheard speech in these games to that in Oblivion and Mass Effect. In both of these games you can listen in on full-length public conversations. I would argue that this approach is simply less successful.
Those full conversations are, first of all, a bit "uncanny valley," since in reality the speakers would stop talking or turn to you as soon as they noticed you just standing there ... awkwardly listening in. (And Assassin's Creed does in fact feature that sort of reaction!)
Worse yet, they come while you're in the middle of gameplay (exploring, questing, or shopping), and they force an awkward decision on the player -- whether to stop and passively listen for a minute, or walk away feeling like you missed something. Neither option is great. This is verisimilitude versus realism in a nutshell: Full conversation dialog might be more accurate, but carefully tailored sound bites capture the essence of overheard speech far better.