There's this misconception that Steam is DRM. Steam is just a delivery system, but Valve supplies tool to implement DRM if developers and publishers want to make use of them. Steam games do not require Steam to run unless it is configured so by the game's manager. Skyrim on launch did not require Steam to run, but Bethesda patched it later. Many older games do not bother with Steam dependency, such as Commandos 2. Move the game folder around, copy it to another PC, launch it from the exe with Steam closed (and Steam will not start up).
It makes no sense to say "We will offer a Steam version and a DRM-free version" because being a Steam version doesn't necessarily imply things one way or the other regarding DRM implementation. Why not make all versions DRM-free, yet still sell the game on both Steam and GoG? Why punish people who choose Steam instead of GoG as their delivery system by giving them DRM in their copy, when DRM free versions will be readily available anyways?