They also want the ability to do rolling updates incase an update is bad. For example, roll this update to up to 1% of users, wait 10 minutes, then roll it out to all users if those 1% don't have worse crash statistics.
It also does diff-based updates, so security patches can be delivered in just a few kilobytes, which is important for all the users on GPRS connections.
Other updaters also don't have the ability to downgrade, either based on the new version failing to start, or based on a message from Google, which might be necessary if an update is bad.
Other update platforms don't let them have fine-grained control and a fast feedback system like that.