I'm with you, Grot. I think most people would say a musician plays an instrument. I guess you could argue a singer is using their voice as an instrument, but when I see a list of the "Best Musicians", I'm assuming they are playing an instrument.
A few definitions from various sources:
1. A person who plays or composes music, esp as a profession.
2. A person who plays a musical instrument, esp. professionally.
3. A person who is talented or skilled in music.
I guess #3 could cover a singer. It's all semantics - it's fine if they want to include singers, but it's not what I think of when I think of a "musician".
To each his own!
walrus