Why Agnosticism?

[Napoléon]

I thought agnosticism had nothing at all to do with theistic/atheistic belief structures and related to the certainty of knowledge?

You're right.

Agnosticism is the view that certain claims—especially claims about the existence or non-existence of any deity, but also other religious and metaphysical claims—are unknown or unknowable

Although the wiki article acknowledges that agnosticism is termed alot with 'claims about the existence or non-existence of any deity' it doesn't say that agnosticism is ONLY to do with 'these' claims.
http://en.wikipedia.org/wiki/Agnosticism