1) Why should "off by default" be the standard and "on by default" a standard violation? Any sane person, especially after consulting with users, would conclude that it should be the other way around. There's no a priori reason to say that "no explicitly-expressed desire not to be tracked" is less valid than "no explicitly-expressed dire to be tracked", since we all know most people just stick with default settings.
The reason is that no one ever intended to actually honor DNT unless it was only used by a tiny fraction of people (and probably not even then), so that's the way the standard was written. Complaining that IE "violated the standard" was a useful way to try and distract from this fact.
2) IE10 violated standards left and right, and most of the time web servers and developers just grumbled and dealt with it. In no other case did anyone commit code to Apache to ignore headers sent by IE. Why different for DNT? Because unlike most settings, DNT actually cost them money. So once again "it violates the spec!" was a figleaf for the real problem.