That can't happen. Steam is dependent on demand. They can only "dictate" what happens to stuff you already bought there. They can't dictate what happens in the future. Also Steam and the indsutry are not the same. But you're right, the ones in power are the industry and not Steam. And in the end, the ones really in power are the consumers, no matter how big Steam is. Steam/Valve can never dictate the industry because in fact nobody needs them if not for the additional services they offer. If people decide that these services don't justify the costs anymore they will refuse to buy there. And the industry can just sell digital goods by themselves without any need of using Steam. You use, it's all kind of exaggerated...
Companies have been doing it for years. Banks are some of the most adept at shaping, driving, and building the public to a control point through monetary products and principals (hint: Consumer Credit), but many other industries do it quite a bit as well. Cloud computing is a control mechanism, shaping the public to a position to increase reliance on bandwidth and creating more services that people will be required to use. Once demand goes up, then slowly past means are pulled away. It naturally occurs and the result is that everyone is eventually forced to it. This happens a lot with politics and laws as well.
Though lets take a relevant example to this industry. Larian wanted to make a turn based RPG from the start. When they began, Diablo was the big craze and action systems were in high demand. During that time, publishers were becoming a problem, asserting too much dominance over the studios by dangling the purse strings. They controlled what type of games were to be made and they shaped the market (read about Brian Fargo and his problems with this). Larian was forced to make an action system for their game and again, forced in their continued titles. Heck, they had to go out on their own, take MASSIVE risks and bet everything they had on the fact that what we saw in the market was not what people truly were demanding.
For over a decade, good cRPGs have been nearly extinct because the publishers controlled what was driven in the market. Making numerous iterations of the same game over and over wasn't a demand in the market. The market complained about it, but they kept buying it because that was their choice. Larian proved this with the success of D:OS.
Consumers are part of the equation, but a large portion of it is controlling the market, controlling the consumer, dictating to the consumer their demands. It really is a mind trip and it is only possible with sheepish shallow people who are easily manipulated (that remind you of any types of gamers?)
You are right though, the market is the one truly in power, but that power is meaningless unless it is exercise and the public refuses to exercise it to any real consistency. So... they continuously get manipulated by industry.
