Apple is bringing its Safari browser to Windows (see Larry's review of the beta). It's a logical extension of Apple's embrace and extend Windows, which began with iTunes. It's not likely that Safari for Windows will make a dent in Firefox or Internet Explorer, but it will be a boon for the iPhone as a platform.
Watch the video clip from Steve Jobs' WWDC presentation on the iPhone and developers
The iPhone, due to launch June 29, will support applications created with Web 2.0 standards, such as AJAX and REST. The iPhone is built on Apple's OS X and includes the Safari browser. Applications developers can create plug-ins or widgets, for example, that work with Mac and Windows Safari and the iPhone, with the capability to tap into iPhone’s services for initiating phone calls, sending email and mashing up with Google Maps.
However, Apple is not opening up the iPhone to native applications, outside of the browser, and allowing deep integration. Nonetheless, it's a friction-free and secure way to get tens of thousands of developers working in an iPhone ecosystem. Smart move.