[spc476]

malloc() is defined by the C Standard. If you want to claim your compiler is ANSI or ISO certified, you need to support malloc() (as well as the rest of the C Standard library).

[pjmlp]

Quite right, except we are then talking about compilers and not OS APIs.

UNIXes are the only OSes were there is an overlapping between OS APIs and libc due to C's origin.