Provision of heavy maintenance visits possibly at a distant MRO and line/base maintenance provision - i.e. A's, B's (&generic MSG 3 or operator derived equivalent), ASB's and engine changes - are two separate issues and and can be considered integral or separate issues/cost bases depending on airline's choice of direction.
As I recall UK CAA for example requires definative provision/arrangement and contract for both as do the BAA with regard to incident mx. support so as they dont get an acft blocking a runway/taxiway/stand etc.