First, it is way too easy to hide information from the PCI assessors. BTW, they are NOT auditors, they are assessors, there is a big difference. But it is too easy to hide stuff because to really dig into a complex system for every last detail is already cost prohibitive.
Which brings me to my second point. If liability gets pushed to the assessors (or SOX auditors which are real auditors) then the cost of being assessed/audited are going to skyrocket because they will just pass the cost of liability right back to the company that hired them. The companies being assessed/audited are being held at 'legal gunpoint' to comply and pay whatever cost. Then, the cost of being assessed will be passed on to the consumers or the company will go out of business.
"Money is the root of all money." -- the moving finger