Virus In Training

Okay, first of all. Like many, my favorite blog on wordpress.com is icanhascheezburger.com. WICKED, LOVE IT LOVE IT LOVE.

But if you notice, right on the header of this blog, there exist adsense!. I thought we cant use adsense on a wordpress.com hosted blog!. What gives? does wordpress allow adsense only on higher profile blogs?, if so, how is that defined? Can someone please shed some light on this.