I think the ref made the right call about the elbow not being a violation of the rule.
12 O-clock to 6 O-clock elbows, has they were originally and time and time again described, are not only being about a 90 degree angle but being brought down from the high 12 o-clock position, as in an elbow or at least fist raised high, like above the head, and brought straight down to the 6 O-clock position. They are described as ceiling to the floor elbows, implying their high originating position.
Looking at the two gif animations,, (edit that, I could of swore the OP had originally posted a gif of the elbow sequence, I'm assuming what I'm saying here was pointed out and it was switched with an image after the fact) (and edit again, the OP confirms he originally posted a gif about 6 or 7 posts down, but now, it is the .png we see today...)
in the first two posts it's very clear to see the difference between short, what I would call 6 O-clock to 6 O-clock, 90 degree elbows and the brought down from high, true 12 O-clock to 6 O-clock elbows Jones landed on Hamill.
Now the part I don't know if it is or is not true is that they made the rule as a response to professional martial arts stone/brick/block breakers using the move to break large quantities of solid materials and the implications of using such moves on fighters in MMA matches.
I don't consider there to be a argument on this, imo there is no legitimacy to the complaints levied towards that one elbow.
In fact, I'm trying to find a this discussion somewhere, anywhere else on the web. Mmaforum.com is really the only place on the web I've seen this conversation take place, even onshitdog I haven't seen a thread about this. Fact that this thread is second only to a site called IllegalElbow.com that has a preview article about UFC 159 on a google search of illegal+elbow+sonnen+forum is enough that I'd shut this fradulent
conversation down to the garbage section for the rep of this site.