German site eGames.de has a revealing interview about the trials and tribulations of modding with arQon, one of the guys behind the Q4Max modification for Quake 4. While it is a little on the rant side it gives interesting insight into the mentality of the modding community, especially comments like the following:

The featureset mods like OSP, Q4MAX, PK++, HL2DMPro, and so on, are simply doing a job that should have been done by the company that sold you the game. Instead, extremely bright, talented, and dedicated people give up literally hundreds or even thousands of hours of their free time, and put up with incredible amounts of abuse from the community, for absolutely nothing in return except personal satisfaction and the chance to play a game that sucks less than it did out of the box.

Anyone that has played any of the old school FPS games no doubt remembers the days of OSP and other mods that added much-needed support for certain features. Obviously though, these features aren't included because they do take a lot of work to create - and most games continue to get sold without them, so it is simply not in the developers (financial) interests to include them most of the time.