I'm only an OJS user. My institution (ibict
) was responsible for the translation of OJS to portuguese, and maintaining a direct contact with the PKP Team to develop what we consider important for our scientific community.
John Willinsky would be the right person to answer your question more appropriately, but I could give you some pointers.
The PKP is a project geared towards providing public access to knowledge that would otherwise be difficult to find. To fulfill their objective they developed a set of tools, as well as use other free Open Source solutions, which are or will be integrated by the OAI-PMH (Open Archives Initiative Protocol for Metadata Harvesting)
Why use OAI? Because science is supposed to be free... Knowledge should be shared. Scientific research has been previously funded, there should be no need for people to pay over and over to access funded research. John would say these thing in a more polished and a lot more convincing way.
Also, there is a need for the common people (those who do not know about the subject in question) to have access to a broader context to what their reading, or else, they would have no means to tell if what they are reading is useful, or eve correct.
At our institution we have also embraced OAI
and Open Source to reduce the cost of research and provide greater public access to knowledge.