Why Flash and PHP?

HTML is much more of a text markup language then it is anything else. This is despite the fact that it has been modified to do more then its original intention.

PHP brings user input and interaction and incorporates it with HTML. Most websites on the internet allow at least some kind of user input and PHP is what delivers that.

Unfortunatley HTML and PHP are both limited in their ability to do powerful visual interfaces or give complex visual interaction to the user. Flash is the only one of these three that allows for complex animations, video and visual effects while at the same time offering a wide variety of connectivity back to PHP and HTML.

Each one has its own purpose and it is usually a good idea to use each one for what it is best at, which means incorporating all three will give you the best results.