Why do people care about feat taxes?

[Silvercrys]

"Meeting Class Requirements: It’s possible for a character to take levels in a prestige class and later be in a position where the character no longer qualifies to be a member of the class. An alignment change, levels lost because of character death, or the loss of a magic item that granted an important ability are examples of events that can make a character ineligible to advance farther in a prestige class. If a character no longer meets the requirements for a prestige class, he or she loses the benefit of any class features or other special abilities granted by the class. The character retains Hit Dice gained from advancing in the class as well as any improvements to base attack bonus and base save bonuses that the class provided." - Complete Warrior, page 16


It's not just the first level; quite the opposite.

That rule doesn't appear anywhere except in CW and CAr to my knowledge. If they wanted it to be universally applicable they should have put it in the prestige class rules for every book they printed after that, which they didn't do, and they never errataed the DMG to include that text despite issuing DMG errata after those books were printed.

It's entirely possible that they wanted to try the rule and then decided not to implement it more widely. It's also possible this is RAI. But it isn't RAW, and for my own part, I don't even use that rule for prestige classes in the books that rule is printed in because the rule doesn't make sense.

I require characters to meet prerequisites whenever they take a level in that class; the only penalty for not meeting prereqs for classes is not being able to advance the class further unless explicitly noted otherwise in the class itself, same as the penalty for Monks who become nonlawful and Barbarians who become lawful.

Is that RAW? No, but it's the middle ground I've chosen for my home games. RAW here is pretty murky, but I don't think RAI can be to apply a rule only found in 2 non-core splat books to every prestige class ever printed. Maybe it is, but I don't think so.