From their facebook:
Went digging online and Holy Hell...their website is atrocious.
Anyway, they just say PC/Mac. Possibility for Steam?
And more recently:
Distribution...Steam, no Steam?
November 24, 2011 at 7:43am
The Pinball Arcade: It shouldn't be too long after launch. We'll just need to spend some dedicated time testing compatibility and get it on Steam (and/or other sites like Steam).
Sounds like definitely not at first, might have to be patient if that is a deal breaker for you. Which is understandable in this case, as the product is built around DLC, so whatever you buy it on, it's worthless to move to another platform as your purchases don't move with you. Maybe they'll find a way to get around it, but they'd have to sell their DLC through Steam directly to put it on Steam, so I'm not sure how'd they do it, unless you got free codes for having bought it directly from them. That, or maybe after a year they'll release a "gold" version which includes 20-30 tables for $20 or something, to get people who had a bunch of the tables already more likely to re-buy it on Steam again.
Will it be released through Steam?
Monday at 5:55pm
The Pinball Arcade: Still not sure yet about being available on Steam.