[Finnucane]

"The two-space convention is left over from the days of typewriters."

And that convention itself came about as an imitation of common 19th-century typesetting style, where more space after punctuation was still fairly normal. Technological and aesthetic changes--the adoption of Monotype and Linotype machines, and the influence of early book designers like Bruce Rogers--started a trend to more even spacing in typeset printed books.

[dnautics]

Im not convinced that the two spaces thing is a typesetting artifact. If you look at the declaration of independence and the constitution, which weren't typeset, there are larger spaces between sentences than words.