Let's check the facts using Wikipedia:

"Thompson received a Bachelor of Science in 1965 and a master's degree in 1966, both in electrical engineering and computer science, from the University of California, Berkeley, where his master's thesis advisor was Elwyn Berlekamp."

"[Dennis Ritchie] graduated from Harvard University with degrees in physics and applied mathematics."

I think that an operating system where you can't rename or delete a file that is open by some process is idiotic beyond words, even without MS-DOS drive letter names thrown in.

To work around the problem by providing a function to schedule a file rename at the next reboot is ironically cynical: you expect the system to crash often enough that this is viable.