It matters because it's there. If it was meant to not be DRM it... wouldn't be DRM. That copy is very much designed to justify the fact that Steam allows games to publish with double or even triple DRM solutions under the Steam platform.
In practice, the DRM matters because it discourages keeping a backup of fully owned game files. On GOG it's trivial to backup offline installers, which are provided explicitly (and I do keep a backup of games I only own on GOG, by the way). Steam explicitly limits your access to your games and how you use them, presumably to support a secure microtransaction environment within the Steam platform. That'd be the "ensures the Steamworks features work" bit in that text.
That's extremely nontrivial for Steam, for the record. Disputing the ability to drive separate MTX under Steam is why several major publishers ended up withdrawing for a bit until they realized it's not commercially viable and Steam is effectively a quasi-monopoly on the PC platform.