I'll take this opportunity to write a mini-rant.
GOG spent years marketing themselves as the anti-Steam (I bought into that myself even if I didn't have issues with Steam), then 3 years ago they decided they wanted to be just like Steam (DLC, regional pricing, early access, etc.). It was expected that eventually GOG would have to start expanding their catalog and focusing on newer games since the well of old games that can be reasonably acquired (legal/licensing issues) was drying up.
The problem is that GOG doesn't have the tools to do anything as well as Steam. Best example is the way they handle patches and updates. Devs can directly issue updates through Steam, but they can't do that on GOG. They submit their new builds or patches to GOG, who then evaluate then repackage the updates. Countless times GOG users are left waiting days, maybe over a week, for updates compared to Steam users getting them instantly. Plus, GOG now has to provide standalone DRM-free packages as well as direct builds for Galaxy client users.
Years ago it was essential for GOG to test older games and ensure compatibility with newer systems, but if they think their support team can continue to be the first line of support on almost 2,000 games they're nuts. GOG support needs to focus on GOG itself and create tools for developers to provide direct support and issue updates without the GOG middleman.
GOG's forums are also horribly outdated. Virtually no developers post there. Steam's community hubs aren't perfect but they allow developers to interact with users, post announcements, make sticky threads, and communicate in other ways. I haven't used the Galaxy client and don't know if it has some features that the GOG website doesn't, but overall GOG has awful infrastructure for updates, notifications, and other communication.
GOG's DRM-free policy was great for some games that were riddled with horrible early to mid-2000s DRM like Starforce or Tages, and in the case of Chronicles of Riddick: Assault on Dark Athena (removed this week) GOG was the only place to get that game DRM-free. I still keep my eye on GOG for releases of classic games. I'm happy more old Sierra titles are coming out after a gap of almost five years (IIRC Quest for Glory in May 2012 was the last Sierra release until recent months), and I'll try to pick them up when they hit deep sales. Better yet maybe those games will also come to Steam, then I can get them in a Steam bundle then wait for GOG Connect.
Regardless, I just don't see any reason (personally) to buy newer games on GOG. Like rcsample mentioned there's the whole "DRM-free movement!" marketing strategy that made people feel like they were supporting a bigger cause, but GOG has demonstrated they'll abandon those vaunted core principles to expand their business. I expect that eventually flagship newer games will require the Galaxy client while older games or smaller indie titles will continue to be DRM-free. I can't blame GOG entirely since a universal DRM-free policy is impractical if they want to be able to sell newer games, especially multiplayer ones, and keep them updated in a timely and efficient fashion.
tl;dr - if people prefer DRM-free games, buy from Humble to also get Steam keys.
