gog doesn't really sell games that are steam only games like humble bundle. if you buy a game on gog you don't need steam to play it. they do have a program in which you might be able to get a free key for steam games that you own to get them on gog and bypass steam altogether. their isn't much going the other way (buying on gog then getting a steam key to play on steam).
if you pay attention to the icons on humble bundle you will see a steam icon for games that you either need steam to play or get both a steam key and a humble download.
i get your apprehension, not a huge fan of steam either, though it is a nice platform with some strong points in favor of it. ultimately using it give the customer more choices probably shouldn't be discouraged.