Yes, it would help show that the term "app" is generic, but that isn't really Amazon's claim. It's a bit more subtle than that. They are claiming that "app store" is a generic term for a store that sells downloadable applications. Apple isn't denying that either "app" or "store" are generic, but rather that the combination into "app store" has specific meaning when applied to the realm of applications that provide a digital storefront to sell additional applications. They might even have a case here, as these kinds of trademark things usually come down to whether or not the public associates the term with a specific source. Basically, it would be considered unfair for Amazon to use the term "app store" if it has a connection to Apple in the public mind, because that would mean that Amazon is technically trading on Apple's reputation. That's what the law would seek to protect, and that might be how Apple could win this case.