Also a nit-pick a hero deity in Immortal's handbook system has divine rank 3 not 0.....
That's because it runs on a different set of rankings. Divine rank 3 there is divine rank 0 if we go by normal D&D rankings, and I assumed most would be more familiar with the latter.
And if we go by pure RAW example, all characters over certain level ascend to godhood through pun-pun-ism. RAW, they should be able to make the knowledge checks required to realize their ability to do so. Even if we go by intent, it is fairly reasonable to assume that a level 15 character has a huge following, enough to grant him a divine rank. Even if we just say "no PCs cannot get divine ranks ever", which is probably against the premise of 3.5 as a simulationist system, a character of level 15 is completely capable of living at his power infinitely somewhere. A wizard 9 does not have too much problems for wiping most societies with careful thinking. A level 15 one isn't far away from annihilating most inhabitants of the material plane.
Then again, I am of the opinion that if we want to run a realistic campaign, it should be done under E6 ruleset, and if we aren't trying to run it realistically, we should not try to apply logic such as what the OP asked into it.