Alexa traffic rankings bias?

I keep hearing about Alexa and how Alexa ranks websites. I checked it out today. My three most "successful" websites are ranked by Alexa. This blog is in the 5 million range (i.e. there are a bit over 5 million websites that get more traffic than this blog).What I found interesting is that my law firm site, redlichlaw.com, at #1,282,824, outranks our traffic court directory site, town-court.com,