I would add that in general you still have to install PHP and an Apache server at the bare minimum to get anything done with PHP. You probably have to set up MySQL too. In that respect you can do some lite DB work in Visual Studio without a separate install. The express editions are free like PHP, and there is one location, www.asp.net
where you can download everything you need. PHP you have to choose from an assortment of packages on the official website, and many people prefer a single installation stack. While easier to install, you can end up spending a significant amount of time research which one you are going to choose. As you can tell, I hate the server admin part of web development, and on that score I find PHP no better, and probably more difficult than .NET.
On the other side, PHP is so flexible that you can accomplish what you want to do in almost any way you want to do it. Many people like this in PHP, and it does make it easier to get started coding. However, it also allows people to wildly violate best practices. I should be clear, I know many PHP developers who are truly top flight and I have a lot of respect for them. However, OOP was developed and introduced in 1979 by some brilliant procedural developers who were intent on improving significant faults in the language. 30 years later it's adoption is still an invitation to a flame war on some PHP forums and mailing lists. I respect that OOP is not necessary for a short two line script, but it's superiority for application development is uncontestable after all this time. In that respect, there are parts of the learning curve of quality C# development that are not about learning this system vs. that system, but learning to develop professionally vs. hacking away at amateurish code. It's certainly possible to write bad .NET code, but the aggressiveness of the C# compiler on its default settings is a fantastic way to learn and require yourself to learn what you're doing and some of the fundametal principles you need on your professional journey. That's absolutely something I like about .NET.
And of course, Imar rocks at explaining it clearly. :)