The link is to a short article at eWeek. In it, the author comments on how much AJAX (and particularly the XML portion of it) can increase network traffic. Since Peter and I talked about that on the show, two weeks ago) I have been finding accounts of such systems increasing network traffic by figures spanning the range between 3.5 and 12 times! That really is a lot. Plus, outside of the increased packet transmissions and receptions, there are significant processing loads on the server side. No free lunch here, folks.
Even so; not all the hype surrounding AJAX is misleading. There are significant benefits to using the technologies in many cases. The problem is one of choosing when these technologies are appropriate to use and when they are not.