Zen:
I think the simple tying of flight to Sailing is
not a good idea.
First, there may be some conditions that would affect one and not the other.
Second, allowing the full aerial move over water leads to other distortions, particularly on the world-size maps where the sea provinces represent huge areas.
Also, my intuition is that allowing aerial moves across a several-water-province barrier is bad for balance.
On the other hand, not being able to make a small jump plays havoc with my suspension of disbelief and immersion.
Thus, a small conflict and a wish.