Desura http://www.desura.com/ alows distribution of games for Windows, Mac and even Linux platform.
As far as I know they don't have such strict rules for validation as their primal goal is also to distribute games which are still under development (great for indie comunity).
Their validation proces is mostly used only to prevent spreading of malicious software (viruses and such).
They alow you to publish as many patches for your software as you want and as often as you want. Only drawback of Desura is that their validation process takes sometimes even more than a weak to be finished, so publishing of patches through their platform isn't best as you need to wait for each patch to be validated and therefore wait for response from your gaming community to the latest patch. But even steam has patch validation the only thing is that their validation proces is usually quicker.
Another advantage of Desura (atleast by my opinion) is that while they do offer special software to alow of downloading, installing and keeping your games updated (similar as Steam client) they don't force you to use it. If you wan't you can always go and download a standalone instalation for desired game directly from their webpage.