I don't think Steam would ever need to be exclusive, especially for DCS. I agree that would make no sense: But there are over 50,000 people playing COD:MW2 on steam at the moment (http://store.steampowered.com/stats/) and they basically paid about $10 more due to the convenience of being it on that platform (rather than via Amazon.com and the disk). People might actually pay more, even than the ED download option?
In the area of strategy games and simulations then Steam is helping that market, mostly through downloadable content, i.e. perhaps DCS being modular could offer maps, aircraft/vehicles on a per pay model?
http://store.steampowered.com/genre/Simulation/
Older games tend to do well too, as people browse back catalogues and 'impulse' buy quite a bit. Hardcore sims like ARMA 2 actually draw quite a following on steam, so it's not all 'mass market' morons :-)