WordPress.com has been running advertising on our free hosted blogs since 2006. Many bloggers do not know this because despite the fact they ticked the box required to get a free blog, they did not read the ToS. Many also do not read features page, or advertising entry in the support documents after registering their username and blog(s). Also note that as the ads do not display to us when we are logged in, and as many use browsers with ad blockers when logged out, they may not realize they are there at all. The only way to get rid of all advertising on our free hosted WordPress.com blogs is to purchase an annually renewable No-Ads upgrade.
No blogger initiated advertising, retailing or reselling the work created or services provided by anyone other than yourself is allowed on free hosted wordpress.COM blogs. E-commerce transactions via shopping carts and the like cannot be conducted on free blogs from and being free hosted by wordpress.COM
The advertising exceptions noted in support documentation are for high traffic blogs that qualify for and are accepted into the Ad Control program, soon to be replaced with the WordAds program, and for extremely high traffic blogs that qualify and are accepted into the paid VIP hosting program. WordAds is for hight traffic blogs on domains. You can apply for WordAds when you have pageviews of 20,000 or more per month.
If you have any further questions about advertising and/or affiliate links and/or ecommerce on a free blog from and being free hosted by wordpress.COM please contact Staff directly using this link. http://en.support.wordpress.com/contact/