I'm glad you are seeing what I'm trying to say. When I was typing about this shortly after the specs & pics were released, it looked like a number of people were just completely dismissing my points.
It does take away parts of a less than fantastic hair sculpt. I don't find any hair sculpts to be very attractive to be honest, but I don't think I'd want to deal with rooted hair so I'll deal with sculpted. But still, the shape and size of all the facial features are still the same, so if the DX10 has a bad jawline, nose, lips, etc. so does the DX13. The sculpt did not get stretched or lose its shape when the DX10 was produced. It's all still there, line for line, same as that DX13 proto. Compare with Luka's shots where he really captured all of the details of the DX10 where other photographers failed.
So I disagree, it is not removed from the basic vibe of the DX10. It seems pretty obvious that they were designed as companion pieces. They not only produced a brand new head sculpt, but also developed a brand new Arnold body. Rule of thumb for all toy companies: part reuse as much as possible.
I can't say for sure, but I'm willing to bet that HT wanted to just make a battle damaged T2, but knew that the MMS117 was not up to par compared to EB's work, so they had to develop a new head and body first. Since they had to develop a new head and body anyway, they probably figured they might as well start by making a new clean version to get as much mileage out of the project as possible.
Since there is no different sculpting in that area at all, just slightly wider eye openings, I'd say I'm all but certain it was simply the result of mass production. It also helps the DX13's eyes that the pers sit with less gap between the eyeballs and eyelids. Again, the difference between a sculpt getting one-on-one special care and attention, and getting put together by an underpaid worker on an assembly line.