I think most people (particularly most of the real world, e.g. those outside of FT) don't particularly care, especially since the only relevance the metric has is for lifetime miles which is truly relevant to an astonishingly small % of the flying population. I'm much happier knowing that I'm earning a predictable number of miles for each segment -- even if it may short me a few miles here or there, rather than having to worry about auditing every single flight leg to ensure I got accurate credit based on the conditions of the day. And for me making sure all of the totals line up is far more important than a few miles here or there -- as long as the credit is in line with the program rules.

I know mileage redemption are more revenue driven now but for the sake of argument, let's flip the argument on its head -- what if UA charged redemption (or heck, for that matter cash fares) based on actual miles flown "Yeah, so we had to detour around a big thunderstorm so we're going to need an extra $150 to make up for the extra miles we flew you" -- what's good for the goose is good for the gander, right?