Emacs used to be considered 'expensive' in terms of disk/memory. These days, it really isn't.
Non-Linux unixes are less and less of a factor these days, and even most of those have some sort of packaging system where installing emacs is a quick operation, rather than a laborious download/compile/install.
Emacs itself has remote editing capabilities with Tramp, via ssh that obviates the need to fire up an editor on the target machine in some cases.
If your job involves sitting down at HPUX/Irix/AIX/whatever machines that haven't been updated since 1998, and don't allow remote access, yes, vi is probably a valuable skill. Otherwise, I think this argument is less important than it once was.