I spent a good portion of my youth leafing through Axelrod's Atlas of Tropical Fish and imagining the rare and obscure in one of my tanks! I remember getting the ACA Trading Post (in paper form) and going to the index of "The Atlas" or my other books to try and find the fish I didn't know.
And, of course, marveling at the oddball contaminant in a tank of my LFS (when there were LFS).
Reality is that a single seine-pull in South America can bring in dozens of species that - for whatever reasons - aren't in the hobby.
I think the ubiquity of truly rare fish from Internet sellers (and in fish club circles, in our monthly auctions for literally pennies) has made us take the rare for granted. Combine this with the way that the ubiquity of information from the Internet and you've got lots of fishkeepers who really don't know what's common and what's unusual.
There are fewer exporters in South America than in the past...and we've seen some pretty awesome hobby/online sellers stop operations because the demand just isn't there for stuff that you can't just get from farms / marts.
Matt