I don't think it's a big deal but I guess the author wanted to point out an easy way to crawl this public info. There are similar ways to crawl public Facebook profiles too, so it's really not a big deal.
pete warden tried that and got sued by facebook. they have since changed their robots.txt to forbid public crawling of their site although they still want the google juice so they make exceptions for major search engines.
I said you can _crawl_ in the sense that it's technically possible & easy. Also I don't think you'd get into trouble if you use it for your own research and not disclose your results.
Have you tried it? This was posted in January, but doesn't seem to work anymore.
curl -A Opera 'http://www.facebook.com/ajax/typeahead_friends.php?u=4&__a=1'
for (;;);{"error":0,"errorSummary":"","errorDescription":"","errorIsWarning":false,"silentError":0,"payload":{"friends":[]}}