What a crock...
They're all XML this and AJAX that, and dynamic pages with dozens of database queries each.
There is a time and a place for AJaX - the CMS, it's nice not having the page reload when you toggle the visibility on a product that's being displayed in the nested menu structure (i.e. in the same place it actually appears on the customer facing site).
Back on topic...
First glance at virginamerica.com - no DTD declaration, 11 included js script files (how many were there before?!), 7 iframes - a quick check with Tidy throws up 13 errors, 181 warnings (although they cascade); many unencoded ampersands and unescaped forward slashes (in the embedded js innerHTML) - even the </html> tag is missing! Cobbled together in MM Dreamweaver by a bunch of chimps that call themselves "Web Developers" no doubt... the page still took an eternity to load.
Just out of curiousity I loaded the page in Opera (with js, plug-ins and cookies disabled)... it died horribly; I'm not surprised.
If they really want to "optimise" their website they should consider firing everyone who's currently involved in it and start again. I get the suspicion that this article was posted on el Reg in a journalistic equivalent of "Duck Hunt" - they knew people would look at the source code of the virginamerica site; they knew the it would draw more flak than a day-flight of B17's over Dresden in 1944.