I own No Dead End Web Services and every site we build that requires dynamic data, we use PHP. There is no substitute. Do I agree that we are underpaid, yes....why? Because we can do what others can do much faster and more robust. We can use PHP to talk to other technologies just as easily as those other mentioned methods. I think it's important to keep in mine that PHP is the most popular scripting language available. It does have it's limitations but they are easily overcome.
Good developers deserve good money regardless of their scripting technology.