I'm a web developer in PHP+Mysql. As i can say... worked also with ASP based systems. They lacks some of the facilities that PHP and MySQL (or even better postgresql database) add to your website.Plenty of frameworks are developed on PHP +database connection.
Let say... wordpress, bloggers, youtube, hi5, lot of social networks, lot of directories...
That means something, no?
Name some ASP?
Another tip: htaccess it's a native apache feature, and php deals perfectly with it! (SEO Adicted:D)