As a gamer, there isn't too much I can do about it, except buy games from other stores where the developers offer their games. As a developer, if I'm worried about Valve becoming abusive, it makes sense for me to use more than one marketplace, or a different marketplace than Valve altogether. Since Valve doesn't seem to have a lot of exclusivity deals, this either means it costs more for developers to maintain multiple distribution channels, or they don't think it benefits them to have multiple distribution channels. That said, the continued existence of those other distribution channels leaves the option to leave if they don't like Valve's behavior.

As a gamer, all I can do is support other stores, and I do.