Once again, they aren't discriminating against anyone. They have a policy that one song features a non male in any capacity in the entire night. That band could have simply played a different night.
But, as I said, the problem isn't so much the debate it's people reading what they want even if it's not actually written anywhere. I guess they call that "reading between the lines."
This also isn't about what people find offensive, that was a previous discussion, this is about trying to make things fair - because the free market has failed.