Dear Mr Manjoo,
It’s all well and good that typographers say using two spaces after a period (or after a full stop for the Australians out there) is out of date and unnecessary, but typographers weren’t the ones who taught the vast majority of us about typing. There’s a reason why two spaces after a period persists – a lot of us were taught that in middle school/high school. I’m not old (I’m 31), but even when I was in middle school, we were still using electric typewriters to be taught typing. After years of typing that way, it’s ingrained into my unconscious.
Even as you say, “every modern typographer” may agree on the one-space rule, most of us, even the educated professionals, have probably never encountered a typographer. In the age of computers, desktop publishing, and the internet, the typographer has very little jurisdiction. I- and it looks like a lot of other professional people you have run into- was never corrected in undergrad or grad school for putting in two spaces, so I wonder just how egregious this ‘error’ could be.
One of the things I learned while living and working in Australia is that the spoken and written English language is a constantly changing thing, that is evolving in different ways all over the world. (If you really want to get worked up about something, think about the Aussie/British word ‘orientate.’ It means the same as ‘orient’, so the extra ‘-ate’ adds absolutely nothing to the word. Talk about frustrating!)
Regardless of what typographers agree on, as long as most people are taught at an early age that two spaces after a period is correct, the practice will continue.
If you haven’t read Mr Manjoo’s article, you can find it here on Slate.