I gotta agree with the trees thing
I picked up a copy of the Guide to the World of Greyhawk boxed set at a garage sale somewhere in my middle school to high school days, and that was at least eight years ago. I still haven't read either one of the booklets all the way through.
Part of it is the whole trees section.
Another thing is, my first RPG product ever was the Ravenloft Realm of Terror boxed set. I bought it because, being nine years old and familiar with boardgames, I expected D&D to come in a box and I liked the vampire artwork on the cover.
Once I had a PHB and DMG and understood what a campaing setting was:
I don't think there was a lot of setting there in that old Guide to the World of Greyhawk box compared to Ravenloft. There was some geography, a bit of history that was too boring to read through, some NPC descriptions and Comeliness rules. Ravenloft had an easy to follow history that was cool, loads of nifty NPCs, and new monsters, spells, and magic items (about three of each). Oddly enough, I've never tried to run Ravenloft, and I did run one Greyhawk session to teach some 3e newbs how to play with a module from Dungeon.