And again, they're under no compunction to use ANY rule, variant or otherwise. If you said "my character would like to swap a feat, I didn't realize it's limitations" in 3e or 4e and he said "no", it doesn't matter if the rule is in one core book and one supplemental book.
Agree. I feel like a bit of a broken record here, but I'll say it one more time; the distinction between "core" and "variant" seems a particularly facile and, frankly, kinda vacuous argument to make. PHB2 isn't core, so the problem isn't solved? Huh?
And 4e, I suppose, fixed that, by saying that all supplemental material from here until 5e comes out is
all core? That's the implication here. I'd really like to hope that few gamers are that lacking in iniative, and frankly, gullible, that a designation by WotC of what's core and what's not actually means much of anything in any context other than maybe Living Greyhawk or something.
If I'm running a game, of either or any edition, the only one who gets to determine what is "core" for that particular game is me. With input and feedback from my players, naturally. Heck, the game I'm currently running, I decided that elves, dwarves, gnomes and halflings, as well as any class with a spellcasting progression of any kind was not only not core, but was specifically non-existant in the setting (at least until the PCs could crack the code of the missing magic of the distant past, and maybe get access to taking levels in spellcasting classes again.) Then I specifically opened up hobgoblins, goblins, full-blooded orcs, xeph and dromites as core races, and psionics, and any full class from any of the Complete books as "core." For that game.
I also think the oft-repeated "but that variant rule isn't assumed by any other subsequent publication!" is a major red herring. While true for
Unearthed Arcana stuff, you'd be hard pressed to find a variant rule where that actually made a significant difference to subsequent published material. I would hope that nobody would say that
Tome of Magic is broken because it didn't account for the retraining rule in PHB2 or something like that. And except for
Unearthed Arcana, that statement isn't even true anyway. I recently picked up
Drow of the Underdark belatedly, and I'm actually quite surprised at how many references it makes to "non-core" supplements. It refers to
Underdark many times, and that's a setting specific book fer cryin' out loud. It refers over and over again to classes from the
Complete series. It references psionics a fair amount. It references
MM4 repeatedly. And many others as well. I remember thinking the same thing about
Elder Evils too.