Arguably on a system where you can address 8 bit byte, 16 bit word, 32 bit dword, and 64 bit qword having char, int, long, and long long all be different sizes makes sense (and gives the programmer control) - especially if before they were assumed to be shorter.
A program with 32bit longs will probably work fine most of the time, and save memory while doing it (which can matter for cache hits/misses).
int is the same width as long in msvc though. if the width of an integral type is remotely important to the correctness of your program, you should really be using stdint.h types to document that intention, regardless of whether you care about portability.
They screwed up by letting LONG into their OS structs when DWORD should have been good enough. It would be a huge clusterfuck if long was 64-bit while LONG stayed 32-bit.
A lot of early Win32 code was originally Win16 code - you could in theory have the same code target both. I think that encouraged everyone to favor long / DWORD when they wanted a 32-bit integer even once the 16-bit compilers were receding into the distance.
