I have to admit that I've never really thought of musical instruments as presents, more like the inevitable result of agreeing to them taking lessons. DD (age 6) had a harp bought for her in August, mainly because DH thought the rental/HP deals were a complete rip off. G-Grandma coughed up for that though and I thought grandparents were allowed to do whatever they liked...?
DD probably does get a lot of stuff "just because" but it's nothing very expensive; CDs, books, hairclips; so all under a tenner. She doesn't have a lot of "big" items e.g. playhouse, trampoline, electronic games and I don't think she's particularly spoilt, she certainly doesn't ask for stuff. I think it may be a hangover from my dad's mediterranean background, his parents found the idea of pocket money obscene but would give extremely generously when the mood struck so DD doesn't get pocket money, just bits and bobs when we're so inclined. Christmas and birthdays tend not to involve massive showpiece presents either.