Why Usability is difficult to Sell?

The topic for today is 'Why Usability is difficult to Sell?'.
The main problem that is faced is that it really becomes diffcult to market usability to senior management for a business. For them the main concern has always been the ROI (Return on Investment). Very rightly said in the following article by 'W Craig Tomlin'

7 Reasons you can't sell usability'

First we need to educate and then we need to sell usability.
 Please go through the link above its quite an interesting article.

Some tools for ROI - courtesy Human Factors International
ROI Calculators