So basically what you've said is none of that stuff exists.
Steam sales aren't about the "publisher setting prices", they're about people knowing every day Steam runs a deep discount on a game.
"Up to the developer to implement" means it doesn't exist since there is no common API.
Forums are a requirement -- I always check them (as many people do) before making a purchase. That's a key source of information on support levels, compatibility, and so forth.
And, yes, Clancy, everyone for the past twenty years has had ratings; that's not what I said. Steam has integration with MetaCritic, a review aggregator.
You, like Microsoft, are missing the point of what makes Steam so usable. It's not just another App store. It has a lot of stuff built specifically for games and a culture that encourages purchasing.
Let me put it another way. Valve nailed it in one with Steam. Microsoft gave us Games for Windows Live. Any questions?