This is why you should use stdint.h as much as possible, then you know exactly what kind of integers you're dealing with.
AFAIK, stdint.h is from 1999, and at least one very popular operating system didn't have it until this decade; of the codebases mentioned, according to Wikipedia for instance both PHP and zlib are from 1995.
Nowadays, I agree: you should use stdint.h (or cstdint for C++) for everything, plus size_t (from stddef.h/cstddef) for array/buffer sizes.