The thing is that the period on a typewriter will usually be aligned towards the previous letter, so a "period space" sequence on a typewriter will have nearly the same amount of space as would be seen in a "period space space" sequence on a software word processor when not using a fixed-width font. In essence, this furthers the idea that the double space is an emulation of the output of a typewriter, rather than supporting the idea that it's influenced by typesetting (where in the past the space between words might have been 1/3 or 2/3 the width of the space after a period, if no other space was added throughout the sentence for alignment).
For the most part, the article justifies simply blaming publishers for becoming lazy, though it seems to me that they choice of spacing around sentences is largely determined by the market for which something is being published, and most publishers would have invested at some point in a decent lexer that can handle enough of the burden of finding the ends of sentences to allow the process to be largely hands-off (and allow the appearance of the output to change fairly easily if they want to print a special or mass-market edition later).
For the most part, the article justifies simply blaming publishers for becoming lazy, though it seems to me that they choice of spacing around sentences is largely determined by the market for which something is being published, and most publishers would have invested at some point in a decent lexer that can handle enough of the burden of finding the ends of sentences to allow the process to be largely hands-off (and allow the appearance of the output to change fairly easily if they want to print a special or mass-market edition later).