Just a quick list off the top of my head from the last month or so of my mobile development efforts:
1. The real hardware iPad has a case-sensitive filesystem, and my macbook (and the simulator) do not. This caused an issue in production because I failed to double check the build on the device before submitting to the app store.
2. The performance of 3d-transform based html5 scrolling on a kindle was reported to be orders of magnitude worse than anything I ever saw in the emulator, a fact I didn't really believe until I actually tested it on hardware myself.
You're correct that emulators are getting better and better, but at the end of the day there are still device-specific problems and other issues that only occur on real hardware.