Are you comparing the polished
output (audiobooks) to raw
input (typing)? That's about as unfair a comparison as you could possibly make: I'm positive (from experience) that the audiobooks undergo
massive retakes and sound editing. What you hear is
not a person narrating the whole thing in a single take; the raw input rate (number of words / time spent in front of the mic) is about 20 wpm, if you're really really lucky (you will throw away a lot of material). And halve that for edits, which are unavoidable. Plus the recording happens under ideal conditions, with full and perfect focus on pronunciation.
TL;DR: audiobooks are almost completely unlike voice recognition, you're comparing apples and oblique angles.