Apple was dropped by Samba for purely religious (GPLv2 vs GPLv3) reasons. Trust me on that.
Sun had bought the Procom code and integrated it into their kernel (badly). As for "it even handles ACLs properly" don't make me laugh. I communicate with Nexenta quite a lot. Let's just say there are some ACL "issues" with that code still being worked on (that's not to say there aren't ACL issues with Samba, I work on them myself :-).