There's a bigger difference: Steam competes on "open" platforms (i.e. the major OSes), where "open" means anyone could launch a competing service (and I fully e

There's a bigger difference: Steam competes on "open" platforms (i.e. the major OSes), where "open" means anyone could launch a competing service (and I fully expect another one to challenge Steam in the near future considering the way Steam is heading). No one can launch a competing app service on iOS. Apparently you can on Android, but I'm not sure why no one succeeded yet. Maybe the same reason as no one succeeded yet replacing Steam either, you need some kind of critical mass and that takes time to build.