I wouldn't necessarily say inconsistent use of case as a fault of the OS, but rather a symptom of leniency offered by case-insenstive filesystem. True, you probably won't run into this sort of "quirkiness" from Unix-based software -- mainly because you're *forced* to keep consistent with case because the filesystem is case-sensitive. The case-senstiive nature of Unix filesystem has also been a source of frustration for many folks -- especially if they had gotten used to systems where filenames were not case-sensitive. On the other hand, folks who had gotten used to case-sensitve filenames aren't so irritated (save for the fact that you can't have both an upper and lower-case versions of the filename simultaneously -- though this is only a minor issue as having name that only differ in case is considered bad form anyway).

Of course there's the question if the feelings of any letters are being hurt by Windows because it is being insensitive to them...