Enterprise apps are supposed to be used for private companies to issue apps to their employees, but any developer can make one. In the case of emulators this is usually done by registering the emulator as an enterprise app. This is when you install apps from your web browser instead of the official iTunes App Store. The trick to get most emulators working with iOS is through a process called sideloading. You can still run emulators if you're willing to do a little work and keep your eyes peeled for rogue apps that make it into the App Store. That said, not everyone wants to jailbreak. It's still the preferable method because it's easy to install emulators, ROMs, and use controllers. Emulation on iOS devices has been possible for a long time if you're jailbroken.
Here's how to install emulators on any iOS device, no jailbreak required. Technically speaking, you're not supposed to be able to install emulators on an iPhone to play classic games.
