you should also listed that darksiders require steam to play, cager will appreciate deal posted with as much detail as possible.
also metro 2033 are listed as steamwork on http://en.wikipedia.org/wiki/List_of_Steam_titles.
d2d metro 2033 requires steam according to 1 customer review at d2d
update:
using steam wiki to see steamworks title then match with d2d(if available)w/code and steam is also a deal.
note: some steamworks game(mostly indie games) are drm free which means its not steam bounded unless the steamworks games listed on d2d stated that it requires 3rd party client and not eligible for refund.