I’m not sure I buy into this ‘build in the browser to fuck with Apple’ idea. Steve Jobs evangelizes HTML5 and standards-based development and Apple backs this up by building the the best available mobile browser (which is probably the exact reason Facebook are working with it).
Let’s say Facebook succeeds with “Project Spartan” and becomes a distribution centre for browser based applications. I doubt Apple would be upset by Facebook (a company with unrivaled reach) showcasing the capabilities of Apple’s mobile products. I also doubt that people will stop developing native Apple applications.
If this is a war, it requires Apple to be against the evolution of browser-based application development. I don’t think they are. I think the quality of their browsers is evidence enough for now.