Your title is not accurate. He does not say no to VP. He says it's for Obama to decide and he has yet to discuss it with him or think seriously about it. In other words, if Obama wants him, he'll hear him out and consider it.
That's a long ways from no.
I would suggest to you that the timing of his new book roll out is not accidental. It is setting broad themes for the coming campaign.
So, stay tuned. The meek (namely, the Blacks and the Hillbillies) are about to inherit the earth....together via an Obama/Webb ticket. It's enough to bring a tear to the eye. ;^)
I am serious. I've read Jim Webb's book Born Fighting and love the man like a brother (or a kinsman, since he is my distant kinsman). He has a grand political vision, loves freedom, knows history and will be a great VP. If Obama is wise, he will offer it to him, and thus forge the perfect political-paradigm- shifting ticket -- a union of the historically marginalized of American society (who have oft been antagonists fighting over what scraps there were on the bottom). The symbolism of such a ticket alone would be a force to be reckoned with. It will turn American politics on its ear.