It's based on pretty solid realism.
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Again, grounded in solid realism.
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But I agree in fact with my own examples

When talking about magic it's near-impossible to make realism a valid argument, but I wanted to point out that the
image of the character is also important, and you very rarely see or read about a wizard in armor: whether this is because they hate it, they can't wear it, or they don't want to wear it, is up to an array of interpretations.
I think the original reasons why wizard weren't allowed to wear armor is (a) traditional fantasy image and (b) balance since they were supposed to be weak at defense or to compensate with spells.
Overall I think balance shouldn't be a big issue as it might have been in very early editions... the wizard anyway in 3ed has spells granting AC and can get protective magic items. Maybe in a low-magic items campaign it would make more sense to allow the wizard to also wear armor. But I'd still want to preserve the image...
I'm not saying every single wizard should always be forbidden to cast in armor (in fact the first thing I wrote was that I wished there was a mean to reduce ASF in 3ed), but it should not be the default... it should be rare and it should be balanced by having an appropriate cost. If it has no cost then all rules-savvy players of wizards will use armor and I wouldn't like it, just like I didn't like when (for a while) too many PbP players wanted to play a fighter with spiked chain
Again, skill penalties would likely apply, but, if the ranger is going into a battle, and he knows that he isn't going to need that mobility so much, then why not?
I mean, is this really a bad image for a high level ranger:
If he's not tracking (not in the mere sense of checking the ground for tracks once or twice, in the sense of a continuous activity i.e. following tracks in the wild and chasing the target at good speed) then he can wear all the armor he wants.
In fact, a wizard going to battle also can wear all the armor she wants. In 3ed you didn't even need the proficiency to get the AC benefit, because nothing could stop you from putting an armor on... she is just going to have troubles as soon as she casts spells tho.