It's not a bug - it's a feature: reserved filenames which have special features and functions. And it has been preserved through DOS, and Windows over the years as part of Microsoft's philosophy of "compatibility at all costs".

There are many, many examples of similar (mis)features. Not sure why this particular one is getting so much attention. But yeah, if you know the history, it's not really surprising.

For anyone interested in this sort of software archeology, have a look at Raymond Chen's blog https://blogs.msdn.microsoft.com/oldnewthing/ which is full of this stuff. Very interesting reading.