Even the Steam version does not require Steam to play the game (though you would of course need it for Steamworks functions like the Steam friends invite feature for multiplayer). You would need to use the Steam client to download and update the Steam version. The retail version of the game is Steam; the recent US release should be up to date, so presumably can be installed from the disk with little need to download anything, but Steam is required to finish the install and get future updates.
GOG provides full installers (periodically updated) as well as patches (and there is currently a beta launcher that will download and directly apply updates), while the Mac App store has their own downloader and updater. Neither use Steam.
