DOS required extensions and most early DOS apps just always appended their own extensions automatically and only took in the base name. The system ignoring the file extension made it easier to use the devices in every DOS app, not just ones aware of the devices.
> Unfortunately the API was that you used CreateFile without colon.
I don't have time to do any detailed testing of this right now, but I believe that `CreateFileA("COM1",...)` and `CreateFileA("COM1:",...)` are equivalent, and both work identically. Am I wrong about that?
I'd be more interesting on how the "ignore extension" part happened. Wouldn't be surprised to find some ancient option support there...