Well, with coding that's certainly true. I can spend all day trying to come up with a dozen lines of code. Input speed is not the barrier there. But for writing English prose, at around 90 wpm, my fingers are often lagging behind what I want to say. People can reach short bursts when speaking as fast as 300 wpm. When I get such bursts of thought, it can be hard to hold on to the end of it while I'm still typing the beginning.