I suspect the problem is more significant with refractors. We expect our instruments to arrive in collimation and to hold that alignment unless we have some sort of serious incident - like dropping the scope! We typically don't expect collimate and, if there is a diagonal problem, we often blame the degraded image on poor seeing.
In contrast, serious reflector/SCT/MCT owners collimate a lot and quite possibly manage to null out some errors in diagonal alignment if they are not too bad. Of course there are lots of owners who never collimate, but they are the ones least likely to recognize that they have a problem.
Diagonals may look simple, but building one that will meet specs over the temperature ranges we typically encounter is at art as well as a liberal dose of optical science. I'm just glad the Vic and a few others are willing to do it right. Note that those who do are in the refractor business!
Yep! Any good telescope is just part of a system that can be downgraded by a weak link. However, once I got everything up to spec and well integrated, even complex operational sequences like imaging become much, much easier. Anyway, you have to love that 115!