This used to be fairly true but seems to be less so these days. The lack of an affordable Mac with reasonable power in the lineup for quite a while (plus the quality control issues with the new MBPs) has led to quite a lot of musicians on the lower end of the earnings spectrum to move to PC, while the lack of a high powered, expandable pro Mac has pushed some high end users towards Windows, at least for parts of their workflow.

I’ve anecdotally heard similar things about the video editing world - people would love to use Macs, but Apple took far too long to release the new Pro (and now it’s here, it’s out of reach for many “pro” users who don’t have unlimited budgets), so they had no choice but to move to Windows.