No, I think you are missing my point here folks. The client may or may not understand the difference with an accessible site.
Either way, generally they simply don't want to pay lots for software as they don't understand it - it's not tangible like a book or a car where you can see the quality level right away.
Enforcing standards on developers isn't the answer. It just cuts the web developer's margin and ultimately leads to even lower quality product.
We need customers that are aware of accessibility, understand the benefits of it to their business and are prepared to spend a little more for a site with a higher level of compliance.
Another solution is for the govenment to kick companies with sites that are not compliant, thereby bring the issue onto the corporate radar.
The MOT analogy is very good, because the end user has to fork out regularly to get the car tested and fixed up, not the garage!!!