No, DCS-A10C does not use Steam.
Just a quick note to all who are intimidated by the detailed simulation of the A-10 systems. DCS A-10C offers a "game" mode, where everything is very much simplified, so you can play it as "fly and fight light sim" ala Strike Fighters 2.
There is a very good review up at simhq:
http://www.simhq.com/_air13/air_462a.html