The following is an extract from an interview with Maroon 5 guitarist James Valentine and he makes a very interesting point. See my comments below.
Interviewer: When you started playing, did your parents ever make you practice?
Valentine: My parents made me start taking piano lessons when I was 8 and I hated it and they made me practice piano. I discovered guitar a few years later and they never had to ask me to practice guitar. In fact they had to come into my room and tell me to stop and go to bed. But forcing me to take piano, I think that definitely set up the discipline of being able to sit and practice and I took that to guitar. I think that's important. We sort of need to teach children to do that. I sound like an old curmudgeon now, but when I see kids playing Guitar Hero I think like, "Man if they applied half the time to playing a real guitar that they do to playing Guitar Hero they could be very skilled guitarists."