Double space after punctuation is same though. It's rare to see someone to hit double space after it and it's there on both satoshi's posts and that letter.
Not that rare for anyone older than about 35-40 in the US. I remember myself using double-space and being told to use them in school all the way up through high-school. That changed some time around late 90s and early 2000s. Largely happened through the use of email and message board posting.