|Advanced Edition Companion||240,001||310,001|
|Castles & Crusades||272,001||340,001|
I'm unclear on the reasoning for this. The best answer I can come up with is that different designers/writers have different ideas on how magic-users should progress. They were all apparently pretty happy with the fighter's requirements from the beginning.
I simply can not fathom why the requirements for the magic-user were so lax in the LBB. Something to do with hit dice and a lack of armor, maybe? The only direct-damage spells they have in those books are Fireball and Lightning Bolt. Other than those, magic-user spells are utility, buffs, or just "magicky". So, maybe that's it. An OD&D magic-user winning the footrace to 9th level doesn't have nearly the impact it does when spells like Cloukill and Ice Storm are up for grabs. Not to mention that magic-users from those editions are well on their way to 11th level by the time the Fighter drags his sorry ass to 9th. That opens the door to Death Spell and Disintegrate (neither of which are available in the LBBs).
I guess that explains why it was that way in the LBBs, and by extension AD&D and clones based on those. It seems that other editions/clones woke up to the fact that with access to spell levels 7-9, not to mention many additional spells in levels 1-6, and that there are many more direct-damage spells. Magic-Users under those rules are much more potent and their progression to the strata that grants access to the newer spells should be slowed, otherwise they will definitely come to dominate the campaign, as well as the campaign world.