How can this be irrelevant to this part of the case if this is precisely why, as per Apple, end users don't have standing? The court rejects this argument and points out that who sets the prices is actually a technicality, which is less important than who buys from whom.

Despite what the Apple lawyers claimed, wouldn't the actual interpretation be: Apple could sue app developers? The developers are the ones "producing the concrete bricks" and Apple is the one "directly purchasing the concrete bricks." By arguing this way for this case, and setting precedent, Apple would have been able to manufacture a loop hole by subsequently using the more accurate interpretation.

It's a very healthy precedent for app stores, regardless.

I don't think this true. Look at your bank statements after a purchase from the App Store. You're not billed by the developer of the app, youre billed directly by Apple, so under Illinois Brick, and users do already have standing (obligatory not a lawyer).