I'd say that actually is my point though. If you're a high-ranking official giving a speech, speaking the same language as the general population will make you well-received and well-understood by using the language of your constituents.

Speaking a language people understand is decisively a good thing, and what people understand varies dramatically by situation. "Plain English" isn't always the answer. (Also hierarchy -- when you're on top, you get to set the tone.)

If you want to be part of a club, you need to sound like a member. Unless you own the club.