I asked the folks at WotC about this ages ago. Apparently, it was somewhat controversial and they left the wording ambiguous to let DMs make the decision themselves. It was, I was told, within the spirit but not letter of the rules.
It should be noted, however, that 1) there is a PrCl that explicitly allows this (the aforementioned Kensai) and 2) Monte Cook's alternative version of D&D- Arcana Unearthed (and Arcana Evolved)- included a feat called Hands As Weapons that let you permanently enchant unarmed strikes as if they were manufactured weapons.
It should be noted, however, that 1) there is a PrCl that explicitly allows this (the aforementioned Kensai) and 2) Monte Cook's alternative version of D&D- Arcana Unearthed (and Arcana Evolved)- included a feat called Hands As Weapons that let you permanently enchant unarmed strikes as if they were manufactured weapons.