I think those who love the T1 are among a minority that's defined by a difference in sonic taste - specifically, a taste for sound that's uncolored, neutral, detailed, and quite simply... accurate.
Without taking any surveys and with nothing to go on but my personal assessment of the Head-Fi community at large, I think the majority of Head-Fi, even among those with very expensive rigs, prefer a warmer, darker, smoother, inaccurate sound than what the T1 delivers when using equally neutral and transparent sources.
Even among T1 owners we have people using tube amps, tube DACs, and tube buffers ahead of solid state amps. Why? Because the majority of people prefer a warmer, darker, smoother, less accurate sound.
The T1 is, in my opinion, the only truly "reference" headphone I've heard to date. It's very, very good at adding almost nothing to the signal. And for that, it's shunned.
Excellent post MIke and you nailed it though I do not have the T1's as you know I have the T5P's and I do find using a tube amp and my 801 is a perfect blending match. I could not agree more with your thoughts about head-fi as well.
I have been having a pop at some of the usual suspects of late in the main because I would hate someone new coming to this forum to think that headphone knowledge starts and stops with them, especially the measurement brigade!
I did at first and it cost me a lot of money until I started to read other peoples thoughts who seem to exist on the sidelines and because the Vox Populi around here are so vocal and so into defending themselves and their followers defending them lest another viewpoint be heard those gems of wisdom get lost in the wiz bang of the pyrotechnics that seem to be popular here.
The T5P when I compared to the T1 before purchase is obviously a little more closed in being closed back but on the whole I felt the sonic signature very very similar, I really needed a closed back design and one with lower impedance to match my amp so went that route. I will say now having almost two hundred hours on the 5P's that the closed in feeling is fast diminishing and your right, they add nothing or take nothing away from the signal which is exactly as I wanted it preferring the tuning to be done via the amp and source (NO EQ though!!).