mmap isn't available on Windows. On those platforms it is available on, there could be subtle differences. If you don't care about memory protection, there is no reason not to use malloc.
It's there in spirit. VirtualAlloc is extremely flexible. brk is really intended for a segmented environment but it makes it almost impossible to return commit back to the OS.
A lot of unicies allow over commit because of this where windows will fail the alloc. The windows design is much better if you care about handling OOM.
