Without responding to anyone in particular...
Another point on paladins and monks - these are classes which, unlike any other in the game, have an alignment requirement of "lawful" - which does justify to some extent a "dedication" requirement.
Also, I don't think the big issue is so much (at least IMO) multiclassing OUT of a paladin or monk as it is multiclassing INTO a paladin or monk. I am aware that multiclassing OUT of monk (even without the proscription against other classes) is disincented because things like Quivering Palm get delayed a level... but I think much of the problem comes in "frontloaded" classes... the monk's +2/+2/+2 saves, fast movement, unarmed damage, and so forth are overpowered as a second class. Similarly, the paladin's Cha bonus to all saves, divine health, etc. are overpowered as a second class - compare to, say, fighter, where the only bonus is an extra Feat.
Myself, I would like to see some class abilities be treated in much the same way skill points are treated - e.g., "if this is your first character level, you get X, Y, and Z." If it is not your first character level, you get them at levels A, B, and C."
IOW, the problem - ultimately - is IMO one of frontloaded classes. And because the paladin and monk are both frontloaded AND have cool abilities at moderately higher levels, they are among the "best" classes to multiclass into without restrictions - for instance, a sorcerer might take a level of paladin to maximize his use of his Charisma attribute, then continue advancing as a sorcerer. This is currently allowed - but suppose then he comes along a PrC that strikes his fancy - like a bladesinger - and needs a few quick points of BAB? Yes, he could take fighter, but if he keeps adding levels in paladin, he also gets turning (which qualifies him for even more PrCs) and smites, and other stuff - we presume he's not really in need of the fighter's bonus combat feats. Yes, of course, paladin is a more attractive option now.
I dunno. I'm probably talking in circles. Suffice to say I like the restrictions and see them as a lovely way to represent a Lawful class's dedication requirement - after all, when you're "chosen by the Lawful Gods" you can't just go dilly-dallying and do whatever you want - with power comes responsibility to maintain your dedication. I have considered the idea of allowing a paladin to MC as a cleric of the same deity - but even then, I could see "your calling is not to minister - your calling is to smite" and so on.
--The Sigil