The link between salt and blood pressure is pretty clearly not the one your Dr. tells you, and this has been known for a really long time. Even the first study to show the "link" turns out to be bunk science:
http://www.stat.berkeley.edu/~...
More recent meta studies have shown that about as many papers find a positive link as a negative link between blood pressure and salt - yes, eating more salt can lower your blood pressure (or, more likely, it's all just noise). Look it up on Pubmed if you want to read all the details. It's a good skill: you'll quickly learn more than your Dr. does about any topic of real concern to you, unless your Dr. is a specialist or obscenely good at his job.
What's sad is that simple to understand explanations that lead to simple to follow prescriptions (ie eat less salt) tend to stick around way longer than the scientific consensus behind them.