No, but advertising a game for Steam costs money because you must incur the costs required to use their trademarks in your advertising. I don't think I implied (maybe I did?) that advertising is duplicated, just that it goes up for the more things you advertise it for, due to various usage of associated trademarks and copyrighted materials (logos, etc.).
This game is a re-release for a game that's already released. Effectively you are increasing your advertising budget exponentially because of having to advertise for this game (which is a new release), rather than advertising all at once (360, PC, PS3). You incur less cost if you release it to as many systems as possible this way, because you do not have to pay for a new advertising campaign. Now, you cut costs of development (because you aren't developing a new property) but in general, there is more money to be made in new properties than in old ones anyway. Regardless of what people will say, the Chrono Trigger re-release made far less money than any new Final Fantasy IP.