We aren't talking about a need to turn off intelligence, though, but about the need to choose language (and content) appropriately to the person you're speaking to. Sure, this is not always easy, but that doesn't mean you get to not do it! This - pragmatic language - is something my DS had trouble with in the past; it was on his IEP and at school they helped him with it explicitly. He's much better at it now, but it does take work. IMHO if you're encouraging a 13yo in a belief that this is an unreasonable expectation and he doesn't have to bother, you're not helping. If the person you're talking to doesn't understand, it's not communication. If you know that, or would know it if you paid attention, and keep talking anyway, that's rude, and people will react negatively.
Besides, it's a skill crucial to many careers. I'm an academic, for example: I wouldn't get far if I talked in the same terms to students at all stages, colleagues from all areas and members of the public! One concrete tip: when you aren't sure what level to pitch something at (I meet someone at a party and they say "what do you do?" - do they want the abstract of my last paper, or the one sentence summary of what my department does?) it's OK to ask - e.g. you say "I'm interested in some questions relating to X; have you come across X?" and depending on the answer you explain either what X is or what the questions are.
My career (IT) is one of those in which it is necessary to practice pragmatic language, and I'm one of the ones frequently called upon to translate complicated technical information into a jargon-free format that's easily digestible by the average user. It's something I'm fairly good at.
What I'm referring to is separate from this. It's not the habit of talking over others' heads, it's the habit of conversing in modes and usages that are not commonly heard in everyday conversation. For most people, spoken language is much, much simpler than the kind of written language we encounter on a daily basis. It's language we all understand, and we also commonly hear, just not face to face. Well, for me, there's very little difference in how I write and how I speak.
So yeah, when I was in junior high, kids would tell me I had a wonderful future as a newscaster, because the language I used sounded like what they usually heard on the evening news. My drama teacher even cast me as one in 8th grade.
So that's the choice... speak the way that comes naturally to me, or dumb it down into everyday language. Unless I'm speaking with someone who wouldn't understand for some reason (young, non-native English speaker, mental handicap, etc.), I just don't feel like it's worth the effort. I'd rather just be me.
And that's the quandary faced by a lot of gifted kids. Some choose to dumb down their language to fit in better and draw less attention to themselves... the chameleon effect.
