Roger,
Q1 is fairly straightforward, OSM is issued whilst the campaign is ongoing. Iraq, like SAM, like Granby were all medals issued after hostilities had ceased (the ongoing counter-insurgency in Iraq maintained that medal without clasp).
Q2 is already there, OSM for Afghanistan is quite complex, it is possible to receive the medal without the Afghanistan clasp and serving memory shows similar in the past, Granby could be issued without the clasp and as you say SAM without the rosette to indicate service outside of the combat zone. Your rationale creates more animosity than solves. Some can go to a FOB, never leave it and have fighting soldiers protecting them whilst those in Bastion can be protecting its occupants and possibly be in greater danger than the individual in the FOB, this is why the boundaries set are quite broad.