But that's not true. Actually, it was always proper to just have one space at the end of a sentence. I recently ran across this article in Slate which cleared up the confusion for me. It was with the introduction of typewriters that two spaces were required. The reason was that with type setting, the letters are proportional (that is, an "m" takes up more space than an "l." However, with early and most typewriters, the letters are all the same size and the extra space was to make it easier to read. Not so with computers and word processors as the finished product is proportional like type setting..
After all these years of typing/keyboarding, it's hard to teach an old dog this "new" trick. But I'm working on it. In fact, after I typed this very post, I had to go back and eliminate the extra spaces.
Maybe one day I'll do a post on the Oxford comma which also confused me due to grammar lessons in grade school conflicting with term paper requirements in college.