Apple now has a diverse set of platforms ranging from mobile to desktop to even smartwatch. Apps for those naturally take different forms even if the apps come under the same name. From a user's perspective, however, paying for an app on one platform should give access to the same app on other platforms. Previously, that was not the case as App Store didn't have that ability. Apple is now rolling out the Universal Purchase option but some developers might shirk from at least one note about this feature.