The tiers are aimed at the carriers, not at end users. The logic being that the (typical) end user is not going to be changing to a non-carrier-sanctioned versi

The tiers are aimed at the carriers, not at end users. The logic being that the (typical) end user is not going to be changing to a non-carrier-sanctioned version of the OS. I don't fully understand the difference between tiers 2 and 3, but it looks like the big picture is basically you don't get to put the Google signature apps on your phone unless you enter some kind of agreement with them.