I understand the technical and (short term) economical reasons for your decision. But why do you think that Steam won't abuse its monopoly in the long run? I would be interested why somebody, who is (in contrast to me) familiar with the gaming industry, does not think that a Steam-monopoly is something to worry about.
Whether or not they are worried about the Steam monopoly, they have to think in terms of what makes money for them. Feelings don't come into it.