OK, now you are changing your story: you claimed that it came with a license from the OEM.
However, while you are correct about the license violation, it still isn't theft. Theft requires intent, and there is no evidence of it. Furthermore, this is a civil matter about violation of contract, not a criminal matter.
Had the business owner been given an opportunity to remedy the problem by removing (or buying a license for) the offending software that was inadvertantly passed on to another user, there wouldn't be an issue. He would probably even still be a Microsoft customer.
However, you do bring up an interesting problem: how many people or businesses could meet those requirements? Would your company survive a BSA audit, with no non-compliant items? If you have site licenses, it certainly makes it easier (but that's financially prohibitive for many small businesses). Are you absolutely sure that no one has installed unlicensed software on any of your PC's, or that the unused ones in the storeroom don't still have old copies of software on them?
Of all the clients that I've worked for, only one had stringent configuration and access controls on their PC's that prevented the installation of any software. The user was restricted from writing files anywhere except in their "home" directory (in Documents and Settings\Username). It was fine in theory, but caused a lot of problems with applications that didn't adhere to that rule.
In other words, this has nothing to do with whether the company paid for the software or not but whether they are in technical violation of the license. All of your moral outrate over theft and payment is simply a red herring. You really simply think that Microsoft should have the right to demand that people prove they are innocent or fine them as if they are guilty. That you seem to have no concern that someone may be forced to pay twice for their software doesn't seem to bother you. You should get a job in tax collection. Tax agencies live for this sort of thing.