Actually I read slightly faster than the average person. But I know how to read at high speed if I have to or want to and thus know from experience that punctuation is important to achieve that. Mind you it doesn't have to be correct or complete. A full-stop to mark sentence boundaries is very often sufficient. Other marks are only really needed as additional cues when constructing sentences in order to help make complex phrases clear and thus prevent mis-parsing. Commas in particular are good at this disambiguation. :-)

If you like, think of it as the difference between a 1-pass sentence and a 2-pass sentence.

Wade.