Not to defend Philly here, but doesn't Broadway (and things like ballet and opera) in general have a perception problem that only rich white people can afford those luxuries? I mean it's no secret that there is a huge income inequality gap in this country, and they are drawn at racial lines. I didn't take Pinto's post to mean that no blacks and hispanics can afford to see Hamilton or that Broadway audiences are all white, but let's not pretend that Broadway, especially at these prices, are necessarily affordable for those who aren't making as much money as others, generally-speaking. Now, of course, people from a great range within our socio-economic spectrum can splurge and afford tickets if they wanted to, but when there's a great many things that hold our interests that are costing more now (have you seen pop/rap/hip-hop concert tickets lately?), I can see how Hamilton wouldn't be high up on someone's list, due to financial concerns, as he/she/they will have to be more selective with their money.
Now with that said, as much as I think one's income plays into it, I also think Broadway and musical theatre in general has a public perception problem that makes it skew older and whiter. Again, this is generally-speaking, not saying that there aren't people of all races going to Broadway. As an Asian-American theatre goer myself, I brought friends, who didn't have theatre on their radar at all (for a myriad of reasons), to shows and they are now becoming Broadway fans. So I think it's more cultural exposure, but high prices don't help.