Beer, especially carbonated beer, is acidic. The chrome plating on brass eventually wears off, brass tastes nasty. Tap water is not acidic or carbonated so it's not nearly as much an issue.
That being said, my 2 towers have 6 shanks, all of which are brass, I believe. My faucets are SS. I'd like to replace all the shanks, but I'd rather not spend $240 replacing them all. Maybe some day.