I think a better example for Google's deep integration into android is the "Google Search app" (previously "Google Now") that is sort of a Siri-equivalent: you can talk to it, it can manage your phone, send emails, create new alarms, manage your calendar, assist your transit, even change the temperature at home if you have Nest.

Worth noting that this type of deep integration is totally possible with the Web: you can use many APIs like voice recognition, alarms, etc. "3rd-party apps" from the web can very well integrate deeply with your device, if you allow them.