I don't see a problem with it. Steam provides a ton of service as a marketplace and distributor. The social aspect of steam friends seeing what games you're playing translates into advertising for your game. They allow for regional pricing adjustments so it's not about blocking players from poorer countries from affording the game. And they have huge frameworks for digital item trading, achievement management, community discussion, modding and more. Their 30% cut of each sale policy is unilaterally enforced and in line with the fees charged by the VAST majority of other distributors. They don't make exclusivity deals in exchange for taking a smaller cut, unlike some much less consumer-friendly markets. Their market is completely fair across the board. I think it's also pretty fair to ask publishers not to push that 30% fee onto the consumer, by requiring the price on Steam to not exceed the price on any other marketplace.

That policy is to the benefit of steam customers, because they can be reasonably sure the steam price is the best price (currently) available. It's not about exclusivity, it's about protecting the value that Steam offers to the consumer.