@boogeymonster: Your forgetting that his death also created a dark side nexus over Endor, and he single handedly corrupted Byss into a dark side nexus
Actually already mentioned Byss in my post before my last one. As for Endor here it is.
Any unusual localization, or vergence, of dark side Force energy. These strange locales emanated the dark side of the Force, and were considered focal points of power for dark side users. As such, they were often guarded by Jedi Knights to prevent their discovery and exploitation. Known dark side nexuses included the twisted tree-cave on Dagobah, Halagad Ventor's hermitage on Trinta, and a "stain" of dark side energy that hovered over Endor following the defeat of the Emperor.
--Taken from The Complete Star Wars Encyclopedia