Well, they're "identical" only in the sense they're both network file systems, however, they are completely different protocols implementing (somewhat) similar functionality.
There are others - AFP (Apple Filing Protocol), AFS (Andrew File System), DCE/DFS (Distributed Computing Environment/Distributed File System), NCP (Netware Core Protocol), and more.
NFS is implemented because it's relatively standard in the Linux/UNIX world and was lightweight enough for the chumby. Something like Samba is always a moving target because it's a reverse-engineered implementation of Microsoft's proprietary extensions to SMB/CIFS - indeed it sometimes seems that Microsoft goes out of its way to change their protocols to break Samba whenever it can. We certainly don't want to get on that treadmill.