The convenience factor of Steam is making the DRM argument moot.

Even with titles that I have the option of downloading DRM free, say via Humble Bundle, I will still just go for the Steam key because it makes it easy.

I don't think it makes the argument completely moot, especially for single-player, serverless games like TIS-100. I agree Steam is the most convenient platform out there. If they just took a little extra step to make sure DRM-free games would behave as expected (something like a download link to a guaranteed standalone installer that you can just back up and feel reasonably safe about having forever) in addition to the excellent convenience they already provide, no one could ever beat that level of service. Well, maybe someone could match it and not take 2 weeks to resolve an incorrectly flagged account issue that's immediately obvious to human eyes, then they'd have some competition.

GOG has their Galaxy client that you can use similarly to Steam. Buy, install and play from the client. Play is possible offline. Ofcourse you can still download manually too as an installer.

Much Assembly Required is very cute, looking forward to see what is possible when it is more finished!