+1 ! I wholeheartedly agree - this adds a lot to the immersion factor and the feeling that you're creating your own world. Renaming units is a great feature we find in games like the Civ series and the new Fallen Enchantress.
The game is lots of fun, and the ability to add that little personal touch to units would give the game lots of staying power and re-playability. It's funny, I think sometimes the smallest details are what make a great game. For example, I think the detailed descriptions of each unit in Warlock are superb - it's rare to find that nowadays, it's often left out of other games.
Please please add it to the game.