I always liked Mike's vocal on "Getcha Back". It sounded great on the radio in 1985 and I think a lot of music fans recognized it and welcomed it/him/the group back based on that vocal (and the falsetto part). Maybe Mike wasn't too fond of it. I didn't understand why he handed the vocal over to David during the C50 tour. It seemed like a fairly easy song to sing, not really stressing the voice too much like some of the other BB songs.
I think it was commented on during the C50 but it was a chance for Mike to take a break, not unlike Brian taking the bulk of 'Add Some Music'. It also was a good fit for David. I personally have always thought it great that the leads on some songs are switched and the group can take great pride that
all principle members have contributed live leads over the years. Quite rare in the business really.
edit. I guess Ricky was the exception but did he ever take a live lead? Thats him on 'Leaving This Town'?