Facebook isn't designed as robust as it seems...

My understanding of a robust application is that under strict conditions, it should degrade gracefully. That's why it is a good practice to design from basic HTML, and later upgrade to an AJAX rich version. If done this way, even if CSS, Javascript failed to load, the user will still be able to at least submit few things.

Maybe it is good to simply do AJAX rich applications, since big sites like facebook doesn't consider graceful degradation.