From Diablo Wiki
"17% - Archer (+3 to Amazon Bow Skill Tree) - Ilvl 60, Clvl 45 (magic-only)" Is this correct? Specifically, why is it "(magic-only)"?
The "magic-only" means that +3 will only be found as a prefix on Magic items, i.e. "Archer's Bow...", not as a property on Rare items. I don't know if this also means it won't be present as a modifier on a 'normal' Amazon bow (i.e. no runewords with +3 bow skills as a freebie!)
Elite items can only be found from monsters in Acts 4 and 5 on Nightmare, and then all of Hell difficulty.
This is no longer correct. In the middle of act 3 NM (Kurast Bazaar), just found a Matriarchal Bow. Damaged, but still Elite. Playing SP, patch 1.13, CLvl 60 but (unfortunately) not a Bowazon.