I was stoned last time, but I'm back and sober. Although a little drowsy.
Well the same definition in your first example uses the word acquainted. And since these words have multiple definitions one can say that acquainted means that you've met someone or something, as in a mutual friend with whom you've become acquainted but don't really know. Furthermore the word conversant has a second definition, albeit archaic. "Archaic . having regular or frequent conversation; intimately associating; acquainted." So using that, since we are in the realm of definitions, one can say that to be thoroughly conversant as you state, that one would have to meet or see the thing one is trying to become conversant with.
Second example. "Are you familiar with changing a flat tire?" Well from what we've discussed one can say that you're not familiar with it until you've done it, sure you can read about it, and you might know how to do it on your car, just like you might know how to change into a brown bear, but you're not quite sure where to place the jack on this different vehicle because you've never done it before. Sure you know the basics, but it ain't quite enough for familiarity until you've done it, then you're good to change that particular tire a million times. A druid can change into a brown bear, and he knows polar bears exist, but he can't change into it because he's never seen one to study it, to become familiar, thoroughly conversant. Just like I have no fucking idea how to change the tire of an 18 wheeler but I can change the tire on my car.
Third example. "My friend is familiar with the streets and can drive there easily." Yeah, because he's done it before. I sure as hell don't know how to drive downtown Manhattan, I live in California, but I can get you to Concord easy. Sure, I can get a map, I can study the map too, just like I can study Algebra, but unless you DO IT, then you don't really know anything about the streets of Manhattan, do you?
Look, the reason I interpret the rules like this is very simple. The druid has some OP feats, like Dragon wild shape at 12th level that allows the druid to gain 19 Nat. Armor and total concealment so long as it isn't broad daylight out and a breath weapon that bestows negative levels. HOLY FUCK THAT'S POWERFUL! Now am I to grant a 12th level druid the ability to turn into that just because he know's what it is? Let's say he doesn't have the requisite knowledge score. Can he turn to a more powerful wizard and say "Teach me about Shadow Dragons so I can turn into one." Would that count? Cause that's fucked up. If one of the NPCs in your campaign is a very friendly old wizard that's seen some shit in his life and is willing to talk about what he knows of dragons to your druid then a 12th level druid now has an arsenal of ALL DRAGONS.
What about Cold wild shape or whatever it's called from Frostburn? Suddenly the party has a 12 headed cryohydra as their best friend that can spew 36D6 worth of breath weapons every 1D4 rounds? Not on my watch.
My argument is about having your cake and eating it too, sometimes you just can't do it, unless you know how to bake cakes.