Does documentation factor into this?

If I can touch-type at 120WPM, then I can churn out a great deal more documentation per unit time than another engineer that can only type at 40WPM. It's less burdensome for me to document well, to write expositional documents and to communicate regularly than my colleague that needs to budget their typing more carefully.

While I might not be bottlenecked when working on a tricky piece of code at 40WPM, I'll likely be bottlenecked elsewhere often.