Yes, I learned this convention when I took a keyboarding (i.e., typing)
lesson in high school. Sometime ago, a style manual for word processing
appeared, and one of the advice is to use only one space to separate
sentences. The reason given is that in a justified format, those two
spaces can become four spaces, or even more. Anyway, a lot of text now
has one or two spaces between sentences, and this wouldn't be a
reliable indicator of sentence boundary. 
Cheers!
basi