I often photograph architecture, landscapes and artwork, in the past I was photgraphing archaeological digs and using those photos to help produce maps. So distortion *is* something I find very important (I usually hate most zooms mainly for that reason).
While I haven't done any more "pseudo-photogrammetry" since I started using the Zeiss' (the Micro-Nikkor 55 2.8 was my favorite for that), for my uses, their distortion isn't noticeable (FLs above 18mm - from 25mm on: I have no 21mm).
For example, I use my Zeiss 25mm for achitecture without a thought, while my Nikkor 24mm was practically unusable. The Nikkor 35 2.0 also fared pretty poorly.
The digital crossover intent & poor distortion correction in the newer Zeiss' could be... It'd be interesting to see some reliable measurements (Zeiss does publish thiers, though how reliable they are & how to get other manufacturers' for comparison is the question).