Micromanagement = a part of the gameplay that a particular player does not enjoy.
If we were to remove all aspects of the game that met some players definition of micromanagement, we would be left with a fairly simple game.
In CIV IV and prior versions:
1. The player had to split his production between buildings and units, etc., his military units between naval, land, and air, but also split his naval units between combat and transport.
Another strategic choice of how to use limited resources.
Part of what makes this a strategic game.
2. The player had to position and use his naval units to their best advantage, including transports.
3. The player could see a naval attack was possible if a potential enemy was massing transports. Think Napoleon or Hitler trying to invade across the English Channel.
In CIV V, it sounds like in some cases an enemy can attack across a moderately wide body of water with little or no warning or preparation.
In CIV V, it sounds like, unless one has enough units to block all possible water paths, bodies of water do not pose much of a barrier; even then, the enemy just needs to punch one hole through your attempted blockade (one unit per hex) in order to launch a massive invasion.
4. A player had to be very concerned about losing his transports, particularly if they were loaded.
5. A player who was about to be attacked or had just been attacked, could focus on destroying his enemy's transports, particularly if they were loaded.
Sounds to me like this change in CIV V is a huge step backwards.
Is it realistic? Don't care.
It removes not-fun micromanagement.