I think there is a difference between quadding spells (wiz/druid) and the mage aoe rain spells.
A quadding spell is clairly defined, by example :
Wizard lvl16 :
http://wiki.project1999.com/Pillar_of_Fire
Creates a pillar of fire, causing between 68 and 76 damage to
at most 4 creatures in the vicinity of your target. This is a wizard's second quad kiting spell.
Druid lvl5 :
http://wiki.project1999.com/Invoke_Lightning
Calls down lightning from the sky, causing damage to
your target and up to 3 others nearby.
Now, why in mage AoE spells desc, there is no mention about the fact it only hits 4 targets ?
Lvl12
http://wiki.project1999.com/Column_of_Fire
Conjures a column of fire that burns
several creatures in the vicinity of your target, causing between 49 and 51 damage.
Lvl12
http://wiki.project1999.com/Rain_of_Blades
Conjures a rain of blades that assaults
all creatures in the vicinity of your target, causing three waves of between 26 and @1 damage.
I've made a lot of tests, the PBAoE spells are the only ones that can hit up to 25 targets.