Actually that raises a question about how many rulebooks each edition released per year, versus how many primarily fluff supplements (setting specific or otherwise) were released for each edition. My experience is a bit too brief to make a call on the top since I missed 1e and 2e entirely.
Is 4e producing a much higher number of crunch-heavy rulebooks versus previous editions? Or is it just my perception that it is?
Martial Power, Arcane Power, Divine Power, Monster Manual 2, Adventurer Vault 1 & 2 and PHB 2 are all crunch heavy supplements. (If you have DDI, don't bother buying it)
Open Grave, Draconomicon, DMG1, Manual of the Planes, Eberron and Forgotten Realms player guide are mostly fluff but have interesting crunch for most people (races and classes)I guess (The first 4 are all definite DM buys while the latter two are definite player buys even if you have DDI IMO)
Campaign Guides are all fluff.