In linux, how can I determine the default text editor, terminal, etc?
does it vary by distro?
I don't think that the notion of default editor or terminal makes sense. For the editor, there is the convention of using $EDITOR when it is defined.
On Debian and related (e.g. Ubuntu, Mint) you have paths like /usr/bin/editor and /usr/bin/x-terminal-emulator symlinked (via symlinks in /etc/alternatives/) to some system default.
See also Dacav's answer