Turns out many players still had floppies. Whoops.
https://learn.microsoft.com/en-us/windows/win32/api/errhandl...
I only put "correct" in scare quotes because it is kinda lame that this is still required. When was the last time anyone was happy that they got an "Abort, Retry or Cancel" dialog?
In the ‘80s and ‘90s one of the most popular PCs in Japan was the NEC PC-9800 series. These were x86 machines but were not IBM PC compatible. MS-DOS and Windows supported them, but didn’t hide all the differences from IBM PC compatibles from apps.
In particular, the boot drive was A: so a system with two hard drives and a floppy would usually have A: and B: be hard drives and C: be floppy.
That really confused a lot installers that assumed hard drives always started at C: and that A: and B: were always floppies if they existed.