Sure, but to most developers the functionality of seeing their mobile application running on their desktop machine is "emulation". And they probably don't need true emulation, they just need to test their application
But for general everyday development, I much prefer the simulator - I can look at the result of a code change in under 5 seconds with a simple keystroke, and not even have to pick up a device off my desk. It's empowering to be able to tweak your UIs and see the results in almost-real-time. I cannot do that if I'm forced to push the app to devices every single time.
Not to mention the debugger runs a hell of a lot faster on the host machine than any device - for the vast majority of bugs that isn't based on device quirks, it makes them much quicker to isolate and resolve.