Interesting! And quite ironic of Ender to claim that the double space is being eliminated by the "computer age." I have never been told anything about whether we should have a single space or a double space at the end of a sentence. I guess it's not terribly noticeable in handwriting, so I never really thought about it.
It would be unnatural just to "guess" that there would be two spaces, so without thinking about it at all, when I first started word-processing (I was about 14... so computers really weren't part of my punctuation education
) I assumed there was one space at the end of sentences, but I noticed that I was always corrected! And since I type quickly, I got in an habit of quickly tapping the space bar twice at the end of any sentence closing punctuation. So MS Word drilled this convention into my writing, and I have followed it since. And I don't think I've thought about it since I was about 14, when I was forced to change! :O