What is it about the SET architecture?

What is it about the SET architecture that makes them sound special? What measureable qualities distinguish them from other designs? Do they have more or less distortion than other tube designs? How about pitch/time/phase accuracy? Can anyone point me to articles about this?
Here's a good one that hits right at the heart of the matter.

These are 2 articles that go together(Part1 and Part2)
Part1 - http://usuarios.uninet.com.br/~edelima/WBsezout1.htm

Part 2 - http://usuarios.uninet.com.br/~edelima/WBsezout2.htm

They should give you some things to think about. There is alot more to this than initially meets the eye, which is why more people don't get this. Instead, it is called "euphonic distortion" by those who don't understand that "systems interaction and distortion" is equally (or more) important than individual component distortion specifications that were taken on a bench with dummy loads . No component operates alone in the audio system. It is the cumulative real-world result that is important. It is in this regard that SET architecture shines, especially when combined with Single-driver loudspeaker systems. However, it is very important that very high-quality output transformers are used in SET amps, since the output trannies are typically the limiting factor in the amp's performance, especially at lower price points.
fewest parts
no global negative feedback
2nd order distortion
to name a few things.
The first two can relate directly to your Q on time/phase.

I remain,
Thanks for the responses--they were exactly what I was looking for. This is the kind of thing that makes Audiogon so special.