The issue for 'realism' for naval bombardment is a little more complex than it may appear.
In WWII, naval bombardment was often far more effective than expected, for instance, the use of Destroyers' smaller guns at Anzio. Conversely, they were usually less effective than thought (Tarawa).
Sometimes, timidity of cammanders made them less effecitive, which is the issue behing the Gallipoli affair.
The key for CIV and most wargames is range. It makes sense they can bombard city defenses, since most coastal cities are actually right on the sea. Conversely, the road or mine in the coastal square may be too far in-land for the ships to be effective.
But don't overlook timidity. Very few battleship commanders will allow their ships to get near the shallow waters of the shore -- and if there is coastal defenses, its even worse. This is why small fire as an Anzio was effective, and the British retreated from Gallipoli on the heals of victory.
So I can name 15 wargames where battleships can attack the coast and not the units inland -- its a matter of the size of the hexes.
Obviously, the advent of missle fire and good tactics can change things. The New Jersey was pretty effecitve in Viet Nam. A more modern missile firing ship can do damage furhter inland.
But given historical reasons, I don't think its unrealstic to allow ships only to bombard the city.
Best wishes,
Breunor