It's designed with security in mind, so your HomeKit fridge isn't going to take part in a DDOS attack [1], and it doesn't require an internet connection. Some people viewed this as the same ol' Apple focused on devices while the world moves on to cloud services, but it turns out that's a big advantage too [2].
[1] https://arstechnica.com/information-technology/2016/10/doubl...
[2] http://www.businessinsider.com/nest-thermostats-go-down-2016...