This is no different than CD keys back in the day. It's really not that crazy of a compromise, and you don't have to validate your games once a month like you do Steam.
Also I think GOG's working on a linux galaxy client, aren't they? Maybe the linux version of SSBD will be released once it's finished.
Simple CD keys were better, because you didn't have to connect to another computer to validate them and they couldn't revoke your permission to play the game. That changed eventually as things became more and more intrusive. If I wanted DRM I would just use that other online store.