I was at my LFS, probably one of the best fish stores in the philadelphia/delaware/new jersey/new york area. But anyways, I go to ask a question about dirted tanks and they had no clue what I was talking about! Never even heard of one! Are they that uncommon or what?
It's not a particularly common technique, but remember that the majority of FW aquarium keeps never really delve extensively into planted tanks, so there's really no reason that joe shmoe at a LFS would know about it.
Algae creates 75% of the world's oxygen, so really we're all just doing our parts...