One practical difference is that you can make dollar bill detection relatively robust. Sure, you could cut it into 4 pieces and scan them separately, but you'd still get stuck when it comes time to print them. There are only finitely many dollar bill shapes. But there are infinitely many plausible gun components, and infinitely more ways to divide them into sub-assemblies.
There is a pattern of yellow dots on the currency. I do not know at what size they tile across the paper, but the piece of currency would have to be smaller than that, most likely.
Far easier to dump the firmware and NOOP out that algo.
