Ok, I'll bite... this kinda sorta sounds similar to the Apple %30?
In any event, say I NEED to sell my game for $25 (IE: I get $25 per sale) and with Steams %30 markup it would be listed on Steam for $32.50.
So lets say some OTHER online digital store only has a %10 surcharge and would only charge $27.50 for the SAME game.
From the article, it sounds like Steam would get very mad about it and threaten to delist the game on Steam.
To be competitive different sites ought to be able to have different overhead percentages (IE: markups) for products listed.