That is why I largely passed on the winter sales, except to gift a few games to my brother. I couldn't help but laugh that you were essentially playing games you never played to get achievements for coupons to buy more games that you would never play. At least it helps developers get their foot in the door. There is still room in the PC gaming marketplace for a small development studio to make a brilliant game, look at the success of Mojang with Minecraft, and lesser known eGenesis with their MMOs including a Tale in the Desert.
So even though it seems "wasteful" to buy so many games that sit undownloaded due to small SSD, it ideally is taking a large chunk out of piracy while giving smaller devs opportunities to turn a buck.