Why do I need this? Well, first of all, this version of the WebPI installs the community version of PHP. Additionally, instead of going to several different websites to download and install Microsoft's web products, you can now seamlessly and quickly install them from one website - and you can update them from this website as well. This is the simplicity we have been aiming for - one website, one download, and simple updates to the best products for building web solutions.
The Installer includes a "Community Version" of PHP rather than a customized "Microsoft version" that allows for current PHP applications to be ported to the environment easily. Their Windows Web Application Gallery has also been updated with several new PHP-based applications that can be dropped right into the WebPI environment and used. You can find out the details about all of this (and more) on the Microsoft Web Platform site.