Hi Renato,
The content of dct:modified could also be manually updated whenever there are significant changes in the underlying data. In the worst case it would always show us the provider's creation date. But then we should probably have dct:modifed and dct:created...
I can't remember if there was any specific reason for not including both DublinCore fields. Anyway, it makes sense to have dct:created and dct:modified, doesn't matter if optional or mandatory.
I also dont remember, but I think it was because Markus just looked for the dublin core concepts that matched the previous concepts we had. So probably we haven't even consider it. I really dont mind adding it, well I mind because we are feature freeze already, but apart of this I dont mind... maybe I tend more for optional than mandatory because, again, when something was created can also be difficult to figure out. Let say that I update my provider software, if the software doesnt take care the creation date will be "recreated".
Javi.