By putting the phone into your browser, you can access much more data as you make a call.  You also complete the separation of phone from device and phone number.  You can now use any browser to make or receive your calls.  There is all sorts of additional data that you might want to bring into a call.  Combining all your messaging apps so that you can see your history of all the messages that you have been sent, or easy access to your address books and favourite contacts.  You might even want to see different data at different times of the day.  You might also want your phone system to integrate with your diary and other apps as well.