Personally, I can generate concise statements (and I'm good at it when I try), but the first couple of times I verbalize an idea I'm usually somewhat verbose. I make an explicit effort to figure out a concise way to say things once I've noticed that I'll probably be expressing the same idea again (and when I write). Perhaps other people become significantly more concise over time without effort, but I'd estimate my baseline compression rate is only something like 10% (whereas when I explicitly compress I can often get 30% or better).
I think the difference is that some people think very verbally and linearly, whereas I tend to think more visually and abstractly. A lot of the time, I have to translate the ideas in my head from these somewhat amorphous concepts or visual ideas into English (or German, or code, or whatever).