Plus, like, 80% of the T3 classes are from non-core sources. Dragonfire Adept? Non-core. Binder? Non-core. Factotum? Non-core. Totemist? Non-core. Incarnate? Non-core. Crusader/Warblade/Swordsage? Non-core. PsyWar? SRD, but technically non-core.

Isn't the only core T3 class the Bard, which argueably is the class that gets the MOST boosts from non-core material with Song of the Heart, Inspirational Boost, Dragonfire Inspiration, the Sublime Chord PrC, etc.

Since T3 is considered the "sweet spot" of balance, this encourages BANNING core base classes in favor of non-core base classes to keep (relatively) balanced characters.