@SailorJerry - I think this goes all the way back to the idea of the Senate as the American version of the House of Lords versus the House of Representatives as the House of Commons. The founders envisioned a House of Representatives full of riffraff (not sure I disagree with them there) and a Senate full of "gentlemen." Remember that in the old days, senators were actually elected by state legislatures rather than directly by the people.
So senators are assumed to be upstanding sorts who would not derail a nomination for personal reasons like that.
And even if that reasoning is no longer valid, senators do still have reputations to uphold. If they hold up a nomination that a lot of other people are for, it will hurt them politically.
And to answer your first question (working backwards here!) I think the logic is that a nominee is best known by his home state, and if they don't want him, no one will want him!