Birthday wishes are special things. They're a form of magic generally dismissed even by the most open-minded of people. Those same people that regularly check their horoscope – or in some cases, hunt the unquiet dead – will laugh off the suggestion that a wish made on the anniversary of one's entry to the world has any power beyond that of a wish made any other day of the year. 

"A body swap has Dean seeing a Sam he'd thought he'd lost forever."