At first I was skeptical that this article was without bias regarding Wordpress.com since it was Matt Mullenweg's own blog that referred me to the story. I was pleased to discover that the author, Jonathan Bailey, helped erased my skepticism in his well written article, Wordpress.com is Virtually Spam Free. The first two paragraphs should get you interested in reading more.
A recent study by WebmasterWorld found that an estimated 77% of all blogs on Google’s Blogspot service were spam. Similarly, AOL Hometown, had well over 80% of its results turn out to be spam. Even MSN Spaces, which as not mentioned in the report, is claimed to host an estimated ten percent of spammer Web site.
It seems as if nearly every major free blog hosting service has been either overrun or nearly overrun with spam. However, one services stands alone, a relative oasis of spam cleanliness, Automattic’s Wordpress.com. Despite being just as free as its competitors and placing few restrictions on registration, Wordpress.com has not endured the spam avalanche that other services have.