In my role as a Visual Studio Team System technical specialist I spend a lot of time talking to customers about quality software - after all the product is designed with this in mind. Naturally most customers are very keen to increase quality - but only if it can be done on the cheap..... Unfortunately this is a rather simplistic view and does not consider the real cost of quality.
Its true, there is a cost associated with building quality into your applications, but there is also a cost associated with not having quality! If you sum up both cost functions you'll end up with the 'total cost of quality' as shown in the diagram below. As the graph clearly indicates, both ends of the spectrum - no quality or too much quality - are undesirable.
The goal must be to work towards a sweet spot where costs balance each other out.