Observations I've made based on the data:
Magic items were not rarer in AD&D1 than they are in D&D3. In fact, by the same levels, a party will probably have quite a bit more magic in AD&D1 than in D&D3. But D&D3 allows the PCs to tailor and customize their magic items to better suit their needs. An AD&D1 fighter may have a +1 broadsword, a +1 spear, a +1 handaxe, and a +2 dagger at 5th level, but the D&D3 fighter might have his preferred +2 greatsword at 5th level. (A quantity vs. quality issue?)
And especially things like potions and scrolls. Note how the poor AD&D1 illusionist in this data doesn't find a scroll until about 6th level, and it has only one spell. A D&D3 spellcaster can have a handful of chosen spell scrolls by 3rd level, either by purchasing them or scribing them personally. But AD&D1 spellcasters just got what they found.
D&D3 characters do level up a bit faster than AD&D1 characters, but not extremely. D&D3 leveling might be ~20% faster, by the written adventures. (Although will this rate continue when we compare higher level adventures?) I suspect that what many people remember as very slow leveling in AD&D1 is a result of DMs not including as much treasure in their campaigns as the official adventures (and the rules as written) include (and assume). For instance, an official adventure might have 1,000xp worth of monsters and then 9,000gp as treasure (for a total 10,000xp). But an individual DM's adventure may have 1,000xp worth of monsters and only 2,000gp as treasure (for a total 3,000xp). Thus leveling was slowed greatly. But this is an effect of the DM, not the rules.
I remember doing this when I ran an AD&D1 game. It was not my intention to slow advancement, but thinking back on it now, that was a byproduct of my style.
Anyone else's experience support this?
Quasqueton