wordpress.com is high traffic web site with Alexa rank 49. They don't have any advertisement on the web site or send mail to users with any advertisements. There is paid blog, i think most of the users will be using free blog. Many users who is ready to spend money can get their own blog installed on their domain easily. How they make money to pay for hosting and other expanses ?
Well, firstly Wordpress although is free for most, there is the Premium Services which are not free http://wordpress.com/products/ Wordpress is a product of Automattic http://www.Automattic.com which is a web design company where the real money is. Wordpress is a pet project of Automattic.
Automattic (wordpress parent company) raised 29.5 Million dollars last year from private investors like The New York Times Co., True Ventures, Polaris Ventures, and Radar Ventures. More info Here
Wordpress could be an 8-9 figure company if they wanted to. I'm not sure why they didn't monetize heavily on it.
Offering a free service is one way of making money. Just because they dont have many revenue sources now doesnt mean they never will.
Wordpress success is because it is offered for free. If they starts to monetize it, they will most likely see an exodus of users.
being able to edit your CSS files on their servers, Buying Domain name and associate it with your blog/site, Adding more disk space on their hosting service and more, I'm not sure we're talking here about small change....
I don't think vBulletin can complain. They have the best forum software around and people like myself are willing to pay to use it.
make a free product, reach 2 million users, and then they can even do whatever they feel about it and for example displaying ads on those blogs
I'm quite sure WordPress will soon be bought from the bigs , not sure when but I feel it , pretty soon