Let me state a couple of things. First is Step-thru (ladies) bikes are not stolen nearly as often as diamond frames in the US. Secondly, most bike thieves don't have an esoteric knowledge of European womens city bicycles to make them a target, they may be expensive, but they are also often little known. In fact I know they are less theft prone then $300 mountain bikes. Most thieves usually steal mens diamond frame mountain and road bikes. With that said, I am one for buying $100 locks for bikes for a reason.
In addition, bike theft is not nearly as pervasive in the US as it is in the EU. Yes bikes get stolen, but honestly most people i know who were victims of bike theft were pretty stupid about the lock they had for the bike.
This is not necessarily for image. But it is for my own personal comfort. When I say type of design, its more about the position of the rider. Thats what I meant by style. I don't like being arched over the bike and prefer to be an upright position when I ride.