are they randomly placed in areas when you change areas?
ive had inaccessible chests at least 5 times now, most memorable for me were a floating chest in D'Alessio Seaboard and a chest in a massive tree in Ferndale :S
so yeh, random?
Chest Locations
Aegeroth
The Pointless
I think they're both random and intentionally postioned. Sort of like ANet designed multiple layouts for each map, and had the game pick out a layout at random. I don't know why some chests are ending up in unreachable places, that could probably be just the fact that someone forgot to actually check the map to test the layouts.

Aegeroth
pain in the




Electric Sky
i believe chest locations are randomly placed