It's pretty obvious from my picture that the tread blocks consist of two types of rubber. One of which isn't supposed to be there. The pictures you guys posted are exactly what I would expect normal wear to look like, even consistency tread blocks with no steps in the blocks. The only reason I noticed the rim around the blocks is I happened to see the tire in the right light, so there was a slight shadow.
The wear behaviour of this tire was extremely abnormal. It performed normally for the first 1800-2000km. Seemed to be wearing down OK, just like the other 3 tires we were using. I was thinking that they were performing better than I expected wear wise, since they are an "off road tire". Then, within a few days it started wearing out really quickly, like visibly loosing tread height every day.The only reason it even has tread is that the tour finished before it wore down to the casing. This makes sense, if the tread rubber was only a thin layer on the tire, it would wear normally to the point where it was breached and the soft rubber underneath was exposed. At this point the accelerated wear would occur. Interestingly not all the tread blocks are worn evenly, some areas are more worn down than others, and when you look at the thickness of the hard rim around them, it's thinner, i.e. the breach occurred earlier so the abnormal wear started earlier.
I'm very fussy about my tires, I carry a gauge and check them often, I even have an email from Surly with recommended pressures This tire was a dud, defective, not made properly and others out there have had the same issue. At least now we know why, had I needed to keep riding and just worn it right out it would just be a mystery. And, if you were touring and the same thing started to happen, you now know that it isn't going to end well, so start planning for the worst and get a new tire organised ASAP.