Perfect thread... Claiming something like drop/exp is not contributing... and the sample is all hero rare weapons!
Sigh... Now to prove you wrong.
Unit items are really noticeable, no doubt about it.
i have a 30 endu/30 armor godlike (bc1, though my few bc2 items follow the same pattern of costing AP), costs 45 AP, and 30 endu/30 armor/18 exp bonus, costs 52.
lazy links if you don't believe:
http://prntscr.com/2mpvlg
http://prntscr.com/2mpwbb
Hero items simply have lower AP per stat point so it might happen that eg. droprate would be 0.4 AP, but displayed as 0. You should take a look at epics/godlikes, and not +4exp or such low value.
Even my lazy comparison proves that exp/drop count towards AP even for heroes.
rare melee 11 str 10 -> 10 AP
epic melee 10 str 10 exp 16 -> 11 AP (lower battle stat, higher AP).
Seriously it's just a matter of rounding, so if you're lucky to get a hero item with low drop/exp, it won't cost you more AP.