Sarbanes-Oxley (SOX)'s primary provisions only apply to publicly-held companies. One survey estimated that the average Fortune 500 company spent $4.1MM on SOX compliance in 2004 alone. Much of the cost of compliance is static, so a domestic company with ~$1BB/yr in revenue and domestic company with $100MM/yr in revenue could both spend $1MM on compliance, even though this represents a much more significant chunk of revenue to the smaller company.

The costs of compliance (both financial and the operational overhead of having controls in place) can be put off by delaying an IPO and the requirement to make public financial statements.