Though Yahoo mail looks like a web app, it is a dinosaur that is genetically very far removed from modern web apps. It's the coelocanth of web 2.0, and therefore does not fall under techcrunch's radar.
Yahoo Mail is based on Oddpost, which is the granddaddy of sweet AJAX web 2.0 apps. Not only is Oddpost not far removed from today's web apps, it's generally a key source of inspiration for many of the AJAX techniques used today.