what you are saying may be true for now, but Microsoft is really trying to achieve 100% userspace compatibility, ( they set the line clear it is about user space programs ).

I couldn't cross compile simple toy kernel (xv6) in OS X (because I needed to have i386-elf-gcc, which need to compile whole binutils , which really cumbersome, and brew doesn't support it -as far as I looked into it ) but in BashOnWindows , it just works, it maybe a little slow (specially file system operations) but it works like charm. I actually tried to compile linux kernel and running it on qemu, It worked, but compilation (which is a lot of file system operation) was so slow it hadn't worth it.

Nadella (MS CEO) aimed perfectly, instead of introducing some limited amount of support for linux apps, his company tries to port whole ubuntu user space. After this project matures enough, rest assured, it will be equivalent of using linux workstation (which is dream of most developers).