http://www.nytimes.com/2009/06/18/fashion/18skin.html?_r=1

You may not get the timing just right, what you think is going to take 2 years might take 5, but if you bet on Moore's Law you can be pretty sure your time will come. Look at the rise of interpreted languages, virtual-machines, etc. over the past decade. It's not an accident, it's just Moore's Law playing out.

Still, it's not just that machines can now run "AJAX" apps fast enough that limitations in the underlying technologies are marginalized, AJAX is rising again because we've yet to provide a compelling alternative that combines the speed of development, speed of deployment, speed of maintenance patches, speed of market corrections, speed of "virality" (word of mouth), etc. that are supported by using a browser as a deployment platform instead of limiting it to marking up a few physics papers.