A change in style

I contacted my editor last week, inquiring about the current view in the publishing world on the number of spaces after a mark of punctuation.  Like The Chicago Manual of Style, the AP Stylebook, and the Modern Language Association, she informed me that the industry is moving to one space as opposed to two, and in most cases has already adopted this style. 

On her recent podcast, Grammar Girl explains that computers use proportional fonts, meaning that the space that the letter "i" occupies is