Note to the people asking why this matters: Legally, if you take a position in federal court on X (i.e., that it's okay to ban external transactions by apps using your app store), and you are found to be doing not-X in an analogous situation (i.e., setting up external transactions to avoid fees in your competitors' app store), the court can rule against you in the original case...and then sanction you and your lawyer…
There are specific rules that apply to the different types of estoppel, and they would not be met where Apple is dealing with app developers pursuant to the App Store dev agreement in one case and dealing with Google under the Google Play TOS in the other case.
It might be relevant if Apple claimed that Google is acting as a monopolist by engaging in XYZ behavior, but Apple’s lawyers are smart enough not to make such an argument.