As it turned out, the limits on cash payments are not set directly in the US, but I can't fancy any company (let alone large corporation) doing cash transactions on a regular basis, wtf. And the laws are still there, though...
Since you are obliged to report about any transaction in cash exceeding $10,000 to the IRS and FinCEN
Banks are required to report transactions. That has nothing to do with forbidding. There is no law forbidding cash transactions. It's only not done because it's impractical to deal with physical cash in most business situations.
Yeah, that has nothing to do with forbidding, save only for the fact that it essentially makes impossible to transact in cash over $10,000 on a regular basis. Feel the difference...
And the requirement to report is all-around (banks or no banks)
The requirement is on financial institutions and MSBs (money services businesses) in America. It does not apply to individuals. If I sell something for $10,000 cash, I have no obligation to report this on a CTR (currency transaction report), but taxes are another thing. If I deposit $10,000 in a bank, the bank has to file a CTR. If I make several deposits that make it clear I'm attempting to avoid the $10,000 threshold to avoid a CTR, the bank has to file a SAR (suspicious activity report). In some instances, the threshold is $3,000, but for these instances, the MSB just has to record the information and save it for five years, not necessarily file a CTR unless it becomes clear that the activity is being structured to avoid the CTR threshold.