Why is it that an Invoker can Write summon fire and earth elemental (Conjuring/Summoning), and a Conjurer can't!!!It makes no sense.

another question, when in Dorn's deep and you must take the phylactery to Jamoths tomb, when the lick cast animate undead, he does not just summon regular skeletons, other things when doing instead of the normal skeletons and zombies?

I mean he summons higher level undead

Um, last I checked Invokers coudnt do summoning either. Yeah, ims ure of it - at least in BG. Never checked in IWD.

The lich is above level 14 and therefore when he casts summon undead he gets Skeleton Warriors and such - the same should be true of your own mages.