What are you talking about?
Is this some kind of RPGA thing? MY table plays according to MY rules.
Besides, there's been strong evidence that the Compendium is supposed to be used as the basis for RPGA games. The DDI Character Planner is going to use these rules to check if a character is RPGA-conform.
Consistency is a priority at any event where the same game is run multiple times.
Anything less will lead to bitching at a minimum.
It's more critical in the RPGA than elsewhere, sure. As people have lost characters due to cross-table rules inconsistencies.
Understand that the purpose of a head DM is to reinforce one set of blanket rules, as the reason they're usually called on is to adjudicate alleged DM screw-ups.
I've witnessed dozens of events wherein players have complained that they've been shortchanged due to having had to play under a GM who didn't write the game in question, and failed at running it the way it was supposed to be run.
Now where the games are systemless, or one that comes pre-broken (such as BESM), GM fiat is required to run the game at all.
The set of protocols that creates the highest degree of consistency is the one that works best.
Now, sure you can run D&D in a sub-optimal manner if you wish, and there are work-arounds (such as reading PC sheets, anticipating possible PC tactics, and informing them before the session begins of the recent rules changes) but they are unnecessary effort.