The big difference between vi and all the other editors out there is that some version of vi is installed by default in just about every variation of *nix you're ever likely to encounter. Vi doesn't have to be your favorite editor, and you don't have to be a power user, but you have to know at minimum how to edit a file with reasonable proficiency, so you're not completely lost the first time you ssh into a box that doesn't have your favorite editor installed.
Assuming you have one handy that is statically built against the the right libraries for the right architecture and the right OS, and assuming the machine (and network) is in a state where you can get at the place where the binary is stored. But that is a lot of assumptions and I would rather just take the time learn the basics of vi rather than hope that all those assumptions always happen to be true.
