To be honest I've seen very few linux machines with emacs preinstalled, nano seems to be part of the ubuntu default install (maybe debian too?) but isn't on any fedora box I have immediate access too (it is available in the repos). This might be because I mainly deal in servers with smaller installs than most desktops.

I would entirely agree that a lot of vims popularity lies in it being part of the default install on pretty much every unix box ever though. That and it actually being a decent editor once you get over that initial insert mode/command mode learning curve.