The more pressing reasons why Colin usually does 170As are twofold: firstly, if you've flown with one of the others before the 170A he can't then sign you off -- I only thought there was one other 170A signatory, and he was one of my primary instructors. Secondly, for all of his bull, I got the impression that Colin does care about standards, and I reckon if you can pass with him then a CAA examiner will be a cakewalk.
You are right, of course, that most of the 170As are flown by Colin, but I don't think it's that big a deal.