> If a console maker charges 10% of revenue it's OK, but if Apple charges 30% it's illegal?
There no such clear cut on what is acceptable or not. In fact, typically console makers charges much more than 10% but not much companies are complaining about that because it's more negotiable compared to the app store situation. The court may decide how to remedy this, but the decision won't be made simply based on the app store cut but take care of other contexts as well.
The real issue is, Apple has designed their product in order to retain complete control on potential customer facing interactions and is blatantly exercising their market power. The game platforms are usually not in a position to do so. Android might be slightly better but IMO this also needs to be addressed.
> There has to be some reasonable standard you can apply that will make sense across time and across companies/industries. What is that standard?
The existing antitrust framework is already capable of handling this app store situation; even assuming Apple is not a dominant player (which is a very optimistic assumption in favor of Apple; app store is likely a monopoly based on hypothetical monopolist test), tying iPhone, App Store and its payment module already brings significant legal risks. Though it still needs to evolve to address other situations such as Amazon or Google.