Like EA did with Battlefield?

I REALLY do not see Facebook getting the killer app like Half Life 2, or Battlefield like mentioned below on Origin. Besides, that was a completely different time, before anything even existed. Steam didn't pull users away from the number one software distributor, to become number one. It was more of a killer app, just to adopt the concept.

Further segmenting your software between services, is exactly what people use Steam to AVOID. The fact that everything is in one place, no lost keys, no lost disc, is its selling point. It's bad enough I have to also use Origin to play some key games. So I'm certainly not going to further dilute my libraries.

This may or may not work. Ubisoft, EA, Blizzard and CD Projekt Red all have their own stores, not to mention Microsoft. I think the market is pretty saturated.

Maybe my experience is different from the real data, but I seem to remember people originally hating Steam when it just had Half Life 2 and a handful of other Valve things. It was more or less useless (and sometimes actively harmful) until the store was opened up for 3rd party devs, a critical mass of titles was reached, and most of the early bugs were worked out. Half Life 2 was the first game to require Steam, but I wouldn't really give it much credit for the success of the platform.