Valve changed their policy. Well, I suspect they realised something and then created a policy. I don't think they decided one thing then changed their mind, I think they just hadn't thought of it before.
Basically Valve realised that companies were using Steam to sell games then selling the associated DLC directly, cutting out Steam. Specifically EA had clearly started doing this pretty heavily.
Yeah exactly. EA wasn't doing anything particularly reasonable here, they want to leverage Steams userbase for themselves while cutting out the middle man. Sell people cheap base games then hit them hard on DLC content that they don't have to pay out a percentage on. Valve adjusted the policy to prevent companies from abusing it.
I don't really see how thats unfair either. It cost Valve a serious amount of time and money to build the market from scratch while dragging other companies like EA kicking and screaming into the DD age. EA doesn't get to have its cake and eat it too. The terms were pretty reasonable - you can't sell DLC and selectively omit Steam, it has to be given the same opportunity to sell the content that other stores get.
People just bring their own personal biases into it and get all silly about the Valve monopoly, evil EA and so on. The companies could have been named entirely differently and I'd still see where the logical problem in this situation was.