Earlier quoted context omitted.
Sounds like in this case it needs to be a craft union or industrial union: a union made up of laborers of a craft or industry (in this case, mobile app developers). Get enough developers of high-profile apps on board, and now you have negotiating power. If they balk, make a union-controlled app store, threaten to sell apps only on the union store.
Quoted post unavailable.
If you're seriously asking, how about that unions have consistently and successfully fought for better treatment and pay for workers all around the world. Many of the standards we expect today only exist because of union action over the last century or so.
Developers are no different from any other worker in the sense that they have more power as a group than individually. That generally has translated to better conditions, better pay.
As the gp comment suggests, it seems entirely plausible that this same effect would apply when applied to vendors. A union/guild/group of people is more able to exert influence over vendors than any one individual, and vendors have a bigger incentive to keep them happy and address any issues promptly. Individuals are, as the op demonstrates, completely at the mercy of megacorps.