Alexa rankings are usally off and they make estimates sometimes... i guess this time they made a bad estimate ah?
Hi ... the algorithm gives a bonus for visitors, to any site, who have the Alexa tool bar installed or it seems that way. As for usefulness of Alexa, if you know the web biz, you know it's meaningless; if you don't know the web biz, it's a hot indicator of site popularity. My Alexa crashed, a few weeks ago, into the depths of >650,000. I'm always trying to attract new writers and, as I can, advertisers. First question, out of their mouths, "How cum your Alexa is so low? Why should I write or advertise on an unpopular site?" Ugh! If the Alexa is okay, they used to go after the PR. Now that it's a 4, Alexa is the target. Ya can't win and gotta go with non-web-biz perceptions: ultimately, who pays the bills. Ugh!
Right, I could have the world's most popular website and have an Alexa ranking of 99,343,123. Their rankings are based upon browsers which have the Alexa toolbar installed, which means Alexa is effectively only ranking websites from an audience of webmasters/Alexa users...what good that? DP is in the top 100,000 which means it is kick-ass, don't worry. All that could mean is that a lot of the members from DP have uninstalled the Alexa toolbar. Don't let Alexa fool you, just use it for rough estimation.