There is a huge amount of content that is published on-line free, such as, Wikipedias and a lot of scientific journals. However these do have hosting costs which are covered by various means because it is a human right to have access to the content. For example, Wikipedia is funded by donation, and I personally pay for the hosting of this self hosted WordPress site.

The amounts needed per download are tiny.

To take the example of Wikipedia where the content is provided free and the user is not charged. However there are hosting costs for the hardware, administration etc. According to the October 2011 report the total expenses for September 2011 were $5.4M and the number of page requests were 15.8 billion, giving a cost of roughly 3000 pages/$.