I agree - I'm not nuclear at all, but I am electrical (transmission) and there are significant reasons that we give top priority to providing off-site power to nuclear plants even though they have redundant on-site power sources. What we are seeing at Fukushima right now illustrates that need well.
I'd wondered about that myself. They have all kinds of redundancy of generators on site and they all got swamped by the tsunami. Off site, think higher ground, with underground transmission lines would seem to be well worth the additional cost.