I see it as this (after half a bottle of Baileys).
a; Give the whole game + subscription to all PS+ users, thus creating a reason to subscribe and a vocal enthusiastic user base resulting in increased console sales and PS+ being easily accepted.
b; Charge for the disc but give free access to all future SOE MMO's with PS+, thus providing a quality service that is economically appealing , with steady hardware sales increases.
c; Charge £30 for a disc based game people are wary of whilst having a pricey and restrictive subscription model that most won't understand why they have to pay, stop paying, and servers are empty.
Then go free to play for PS+ members , looking like you dropped a bollock and nobody being too interested. Whereas they would have been if that was the plan from the get go.
Sony have chosen c, so we can expect lots of statements along the line of "MMO's just don't seem to fit on consoles" by people wanting to keep their jobs.