When comparing PHP with ASP.NET I always think of comparing an apple with fruit salad.
PHP itself is "just" a dynamically typed language without much of libraries bundled with it. ASP.NET has all the advantages of the .NET framework like type safety and lots of libraries coming with it.
With plain PHP you have to take care of things like how to name your HTML form elements, pass then to the PHP script, register them and maybe put them back to your form elements in case some data is not valid. ASP.NET does that (and more) for you automatically.
Then of course there's Visual Studio including the free Express Edition for web develoment. Try to do graphical editing with Eclipse or the Zend Studio. Or even try refactoring with one of those. No way. Visual Studio does it all.
Of course to be fair, there are libraries and tool for PHP that do those things for you. But they are 3rd party and in my oppinion lack the integrated development experience with ASP.NET and Visual Studio.
Don't think I don't like PHP. In the contrary. I do like it very much and earn most of my money with it (small jobs besides university). Lots of things can be done very much faster and with less code and you can use notepad/pico/... without problems.
To sum up your question: ASP.NET does a lot more than PHP, not the other way round as you were thinking And its very easy to learn. Trying it out can't hurt.