I have a copy of each edition in front of me, and both the glossary entries for 'melee attack' and 'melee strike' are identical in each edition.
The following melee attack feats would be unusable by unarmed characters under the 'natural weapons are not weapons' theory: Cleave, Great Cleave, Improved Critical, Improved Two-Weapon Fighting*, Spirited Charge, Spring Attack (!!), Two-Weapon Fighting*, Weapon Finesse, Weapon Focus, and Weapon Specialization. (*Irrelevant to monks, of course ...) Except for Spirited Charge, this doesn't seem to make a bunch of sense. Not to mention the NPC Monk in the DMG, who gets the Improved Critical (Unarmed) feat at 12th level.
Finally, note that the Magic Weapon spell has a qualification that it cannot be used on natural weapons; this would not be necessary if natural weapons were not weapons. Although it could be argued that this is just a reminder of that fact ...
The following melee attack feats would be unusable by unarmed characters under the 'natural weapons are not weapons' theory: Cleave, Great Cleave, Improved Critical, Improved Two-Weapon Fighting*, Spirited Charge, Spring Attack (!!), Two-Weapon Fighting*, Weapon Finesse, Weapon Focus, and Weapon Specialization. (*Irrelevant to monks, of course ...) Except for Spirited Charge, this doesn't seem to make a bunch of sense. Not to mention the NPC Monk in the DMG, who gets the Improved Critical (Unarmed) feat at 12th level.
Finally, note that the Magic Weapon spell has a qualification that it cannot be used on natural weapons; this would not be necessary if natural weapons were not weapons. Although it could be argued that this is just a reminder of that fact ...