Libraries have to keep their contents in a uniform format to facilitate reading, indexing and searching for their users. Also, the choice has to be done depending on these users' needs. And with a library as open to its customers as the MeDoc library, a whole variety of platforms have to be adressed as clients to the library. So the format has to be something that can be easily read on any of those platforms, with enforcing no or only small restrictions on these clients. Only one format has to be chosen, to avoid redundancy and inconsistencies.
The format(s) used for the library have to be open so implementing services for reading and searching the texts are possible for the users on any platforms, and noone is forced to use (and pay!) any proprietary product ported to his platform due to the marketing strategies of a single vendor.