Bankai9212: Steam is just the defactor store, regardless of how many stores appear one will always be the most proferred.
There is the most popular one and then there is the most popular one that controls a whopping 75% of the market share.
Steam was the first wildly successful online PC game store that imposed their walled garden which became the norm.
But at this point, given their market position, strict limits should be imposed on Steam's ability to dictate terms to developers, customers and other stores.
It's up to lawmakers to force interoperability, impose restrictions and break down corporations that get too large for their britches with anti-trust laws.
Steam has too much power atm. An absence on the Steam store will break a PC game studio atm so we need a body overseeing Steam and telling them "no sorry, you cannot refuse game X from your store on the grounds you gave and if you don't like it, we'll break you up into several companies". And telling them "for functionalities X, Y, Z on your platform here, you will it an open standard that your competitors can use to interoperate with your platform... refuse and we'll carve you up into a bunch of separate companies".