Seriously, have you even looked at WebMatrix yet? You're describing WebForms. This is nothing like that. ASP.NET Web Pages (the web framework part of WebMatrix) is a lot closer to PHP than WebForms or MVC. A whole site in one PHP file? Yah, you can
do the same in a .cshtml file if you wanted to. Really...check it out and don't come back 'til you do!
Hold on, are you expecting people to try things first? Is the internet new to you?