Moving for a child sucks (believe me, I know) but
>>3 is right, there can be reasons for the move. Moving helps a child develop, morally (to an extent), there understanding of the world, socially. I know some people who were lucky enough to stay in the same place for most of their life but got so much to learn about the world (I kid you not, one of them did not know the name of a popular town 15 minutes away from them).
For me after turning 8, my family moved houses once every year or twice every year. It's normal if your friend is feeling sad, when you get attached to something it's hard to let go. But that detachment is what children need to learn, not to stay attached to materialistic things.