Thus, the characters that appear in those positions - including those in US-ASCII - are somewhat "unsafe" in international data transfer
...
Systems that support ISO Latin 1 in principle may still reflect the use of national variants of ASCII in some details; for example, an ASCII character might get printed or displayed according to some national variant. Thus, even "plain ASCII text" is thereby not always portable from one system or application to another.
That's awesome! Hard to believe that systems have worked as well as they have. It's pretty obvious nobody was expecting that one day all computers would have to read each other's data pretty much constantly.
So I guess the question is: why did the DOS developers pick the character that happens to vary from region to region? I guess they didn't know?
As a wild guess, I would say that in the days before the internet made "international data transfer" something a regular person would encounter frequently, the thought just never occurred to them.
Here is some more info: http://www.cs.tut.fi/~jkorpela/chars.html#national-ascii