Actually, it's somehow a slightly different issue.
Somehow Steam doesn't even know it if you own it, e.g. here http://store.steampowered.com/bundle/477/The_Dream_Machine__Full_Game/ it lists Chapter 4 as unowned for me, despite me owning it for a while now.

Anyway, your point is still valid and surely appreciated.
And thank to the giveaway creator you for making a giveaway for this excellent game.