Well, now, let's think about this for a minute. I imagine Tyll gets non-electrostatic headphones monthly for review, so it makes sense for him to buy a "reference" amp to test those. OTOH, how often does he get electrostatic headphones for review? Last time was a couple years ago. Yes, there are a couple coming up: Mr. Speakers, HFM, maybe n3rdling's Orpheus clones if he ever decides to make them a commercial product. The Sennheiser HE-1 and Sonoma don't count because they have dedicated amps. It is less sensible for him to buy an amp that he MAY need to use every few years for testing, which is probably why spritzer gave him one - because he wasn't going to buy one on his own. It would be great if Justin could do the same with a BHSE but considering HeadAmp's profit margins, not very feasible. And the problem with DIY amps, regardless of how good they are, is, only a small fraction of potential buyers is going to have access, or going to build, one, so how do you make sense of a review that uses an amp that most people have never heard and can't get? And that's even without getting into the issue of which DIY version of which amplifier? For the KGSSHV, for example, do you want the mini version with KGBH PS, or a maxi with Golden reference HVPS. What about the LV - Golden Reference or 7815/7915 basic PS? Let's face it, the stat headphone market is a small sliver of the audiophile market, which is a small slice of the overall headphone market (Beats, anyone?).
Now, Bob isn't a reviewer per se, he is a mastering engineer who sometimes uses headphones for his job, and occasionally does a review as a sideline. If he gets a "reference" amp, it is because he needs one for his job, not because he is going to be reviewing a bunch of headphones. IIRC, before he had a KGSS and SR-007 Mk II, he used a Stax SRA-12S (one of their first solid state amps from the 1970s) with Stax SR-3 and SR-5 headphones, also from the 1970s, which tells you how often he replaces amps and headphones.
So, yeah, in a perfect reviewing world, Tyll and Bob would have reference electrostatic headphone amps. And as long as we're at it, I want a pony for Christmas.