Don't get me wrong, I completely agree some things should be set in stone with respect to audits and what have you, but let's consider the facts: a company that's under pressure from whomever enforces SOX but has quite a large volume of cash on hand will generally find a way to alter some logs were they keen on doing so. Even using some sort of feedback loop encryption/hashing method might be circumvented, albeit harder.

Smaller companies won't do it, but the big fish can probably bribe the right people when needed.