As a kid, I knew that the Falcon's wings had been built by the Black Panther, and wondered why Cap wasn't given a similar set of wings, to maintain power parity. The answer is that a fluke interaction between Cap's super soldier serum and a poison antidote gave Cap super-strength in issue 158, leaving the Falcon feeling like the weaker half of the team. He got the wings to make himself equal to Cap once again.
Writer Steve Englehart explained on his blog:
Much like the idea of turning the Beast's fur darker, Marvel decided Cap should become stronger. I did it but stopped talking about it after a while, and the whole concept simply faded away over time.