You get a largely cross platform, consistent UI that can easily talk to outside services without being configured. All of these things help make the application work consistently across the many devices that exist now (Computers, smart phones, tablets, mp3 players, refrigerators[1], etc.) so you really can develop once and deploy everywhere. It also does seriously help the users that don't know how to use their refrigerator[2] so they can look up recipies and plan shopping trips.