Can I weigh in with a completely non-expert opinion based only on intuition (the tyres' behaviour might be counter intuitive - or I might)?
You say the tread depth is shallower towards the edge of the tyre. I would have thought this was a disaster waiting to happen when you lean it over into a bend on a wet road? Sounds great in the dry, loads more contact patch in a corner than on a straight, but in wet conditions, don't you want more tread (more grip) when you're cornering than when you're going in a straight line?
To me this tyre sounds like it gives you great acceleration from standstill in a drag race and makes the bike really unstable through corners (both in wet conditions).
Due to the shape, and the 'squish' mentioned above, the tread gaps close up when the machine is upright so is close to the same displacement in actual fact.
The other, more important part is that tyre material is flexible, so the smaller and stiffer the blocks are at the edges the better it feels. If you have ever ridden a bike with off road tyres on you would feel the flex of the big chunks of rubber when the bike is leaning over and it is err, attention grabbing to say the least. You want the wheel to feel as if it is staying in a constant curve (for the same steering input. bars and/or lean) not a sort of wobble every time a rubber block flexes.
I dont know if I have conveyed what I mean here, but that is the reason, along with you spend less time on one bank or the other that on the center section or center and part of one side, so it conveniently evens our wear.