Refineries are expensive, and new ones are hard to get past the environmentalists. And yes, it would be nice if the Gulf weather didn't affect our oil supply as much as it does--but is it worth the cost to duplicate or replace it? And given the predictable opposition, how long would it take?
A lot less time than the legal battle, that will start shortly. Matter. Of fact I think the nature crowd file their first case a few days ago. http://www.huffingtonpost.com/2011/10/05/groups-sue-to-block-construction-of-keystone-xl_n_996075.html
Cost of the pipe line, is probably 100 times that of a refinery. That is cost effective. So which is the most cost effective. Building a refinery in the north, are a ten years legal fight, and stealing thousands of peoples property by eminent domain.