You could also use forward slashes, like C:/path/subpath, which has worked since Windows 1.0/DOS 2.0.
That's handy when you're entering paths in a Cygwin/MSYS Bash shell, but might not help much if you're trying to parse or otherwise work with existing patgh variables composed with backslashes.
Yes, you could if you were entering them manually, but some apps that generated file names would screw it up. I think they were using some sort of stdlib function to get the path seperator. Forward slash paths working in native windows apps also wasn't quite a given, either. Keep in mind this was a loooong time ago... like windows xp era maybe, even.