I'm unconvinced it's an introvert-extrovert thing. I'm quite introverted, and I'm not confused when a first-person character starts talking; I usually play with subtitles, I pay attention to the story (even if the game tries to distract me), and designers generally have the decency to put dialogue in scenes where it's obvious who's talking (except Bethesda).
In light of that, I like FPSs that try to characterize their lead. The new Call of Juarez: Gunslinger did a magnificent job at it (though, to be fair, the protagonist is also the narrator). The lead character had both colorful panache and a subdued melancholy in his narration, and it all showed in the gameplay. FPSs are a genre in need of such quick, intense shots of characterization--since they tend to be short and intense themselves--and I don't think they can afford go with silent protagonists as a default. I think they are only justified for a very specific kind of story, and it's one most FPSs don't have.
The silent protagonists I've liked have been in RPGs and open-world games; however, in such a game I know the focus won't be on the internal emotional turmoil of the protagonist, and instead on exploration, discovery, and telling the story of a place or a time more than the story of a person. I, or a projected ideal of me, can be the protagonist, but there is an intimate emotional dimension that is completely lost in the process.
In some cases, it doesn't matter: Deus Ex: Human Revolution was the story of a time more than that of Adam Jensen, and it lost nothing; in fact, it wold have been fine if Adam had been a silent protagonist (though his half-whispered rasp really grows on you after a while). But if the story had been about Adam Jensen, newly-minted post-human cyborg coming to terms with his transformation, then having a silent protagonist would have been crippling for the game.
The silent protagonist is like the documentary-style shaky-cam - they're both immersion-building tools that can work wonderfully. But if you use them habitually or thoughtlessly, they're horribly out-of-place, and the audience notices.