Yes it will be a lot less than 30k unique visitors but don't take the 1 million+ alexa rank too seriously. In this case it probably just means that a lot of their traffic are non-technical users that don't use the Alexa plugin. Just installing the alexa plugin in their own browsers could get their alexa rank to 700,000. Just speculation from my experience.
How reliable can be a traffic ranking system based on some freakin' crapw^H^H^H^H^Htoolbar plugin? (I'm genuinely surprised, didn't know that is how Alexa work.)
