This is not intended to be an incendiary question.  I am a music lover
and many of my best friends are gay and musicians, and we have debated
this question together without reaching any conclusions:  It is a
sincere sociological question which I?d be keen to find research on: 
If you were to take a consensus list of the top 20 greatest pianists
of all time, at least 75% of them were either gay, or bi-sexual. 
Obvious examples include Horowitz, Richter, Bolet, Arrau, Hough and
many many others which I will not list here.  There are counter
examples of course, but as a generalisation the statement that most
great pianists are gay does seem to hold true.  The same trend is not
true for other instruments? the great violinists and cellists have no
generalised sexual leanings and the great conductors are, if anything,
huge womanisers, with very little evidence of homosexuality in this
group.  I?d be interested in finding any research into this sensitive
question as to why this may be the case.

They don't even have to be particularly great-- about 3/4 of a band
organization I am familiar with are gay, especially the string
section. It seems like vast swaths of the artist community are
similarly inclined.