为什么PHP开发人员比.NET开发人员便宜？

This is a two part question; firstly, does anyone out there have some insight as to why PHP contract developers would be available at a much lower rate than their .NET counterparts (around a 30% premium for the Microsoft guys)? I have some theories relating to ease of learning and cost of tools and servers but would like to get some feedback from other people.This is a two part question; firstly, does anyo