This "hosting service" is an academic journal. They do not only host the document but also organize review of submitted papers, edit the document for publication, and ensure long-term archival of published works. And - most important for academic researchers - publishing in a respected journal improves your reputation. Once your paper gets published, you essentially sign away most rights to the publisher (see also the comment on Open Access in this discussion thread).

Whether these publishers contribute enough to warrant the high price of their publications is debatable.