Well, in fact the February 1904 Japanese surprise attack took place against the Russian ships moored 'outside' the main Port Arthur harbor, so we can consider that if the ships had been inside the inner harbor, they would have been protected...
We could not make complex handling for a slight exception, so we decided to dis-allow harbor attacks.
BTW, the 1904 attack in the scenario is there, but dealt with as a scripted event (which is feasible in a scenario with pre-set and known OOB, but not in a GC)
