A friend at my first workplace after college told me I was "doing it wrong" by using only one space -- and I can't go back now. I am not Satoshi.
Plus, it's easier to find the end of a sentence visually.
If you go back to older typeset documents - Ben Franklin's, say - you'll usually see more space at the end of sentences.
(I've studied typography and I've hand-set type. I think it's a design choice.)