AC/DC's situation was unique, but other bands that are not reliant upon *one* signature voice have pulled off the vocalist switcheroo. Styx got away with it two or three years ago - but the guy who replaced Dennis DeYoung can't measure up. Fortunately, the band has also relied heavily on lead vocals from Tommy Shaw and James Young (JY is now effectively the only remaining member of the "original" band), who have steered the band away from the power ballad stuff towards a harder rock sound. Only Dennis can sing Suite Madame Blue, though.
When I saw the Styx episode of VH1's Behind The Music I was shocked at how much infighting there was in the band. Apparently, Dennis was yanking the group in a smooth pop/ballad direction, while James Young and Tommy Shaw wanted to keep the focus on rock and roll. When you're a young and unworldly fan, you assume musicians you admire as a group like each other as much as you like them. It hurts a little the first time you discover that in reality, they were constantly at each other's throats.
Glen Burtnik was an able replacement for Tommy Shaw. I thought Edge of The Century was a pretty good album, and loved JY's song "Homewrecker". I often recalled that tune when reading accounts of Monica Lewinsky and Andy Bleiler, with whom she carried on an affair while being nanny to his and his wife's children. It was to the Bleilers that Monica made her infamous comment about going to D.C. to earn her her "presidential kneepads."