I just had a discussion with my fiance about this, so here's my theory of the evening. I tend to be quite pedantic in the manner of my speech, and in my writing. He is quite the opposite and likes to speak in "vagaries" as I term it. He often employs general slang terms to express himself. I find this maddening and, ultimately, in my quest for truth/understanding, I must question him as to the precise meaning of every word.
I will give you an example:
In passing, he described one of my poems as "out there." I am well aware that this phrase means different, but I first think of the literal sense "away from here." I then extrapolate from there and think of every possible shade of meaning he is trying to convey with those two words. I then examine it in relation to all the other words in the sentence and attempt to discern why he, or anyone, for that matter, would use that as an adjective for a poem. I believe that I do this because I miss entirely the tone of voice, facial expression, etc. of the person I am conversing with. I'm sure someone else would be able to pick up on all the other subtle clues that people emit and would not have to subject such a cliched phrase to an exhaustive analysis.
Since I rely solely on a person's choice of words and the interrelation of them, I see all of the possible meanings. Because I think in this manner, I feel compelled to discuss things in extremely deliberate and analytical detail so that whomever I'm conversing with will instantly ascertain the full sense of my thoughts. This matter is further complicated because I think in pictures, so I must translate everything that I see into a far less precise language. Inside my head, each picture is worth far more than 1,000 words. Because a deficit in the ability to comprehend social situations, facial expressions, etc. is at the core of AS, I believe our speech becomes pedantic because we must compensate drastically in this area. We are then perceived as demonstrating "excessive learning" because we are profoundly less adept in other forms of human communication.
The bonus: This style of thinking about language makes me really, really good at crossword puzzles!