My wife sometimes asks me to play a song so that she can sing along, but she wants me to play the melody line!! I say no, no, no. Accompaniment should rarely play the melody line. This allows the singer more flexibility, the singer can start before, on, or after the beat. She can sing grace notes and other notes, not necessarily in the orignal melody line, etc.
Obviously, she might want me to play the melody line, if she is unsure of the melody, but after that no. If a singer wants the melody line to be played while they are singing, isn't this a crutch?
Starkeeper