A lot of US companies are very litigious, and code can be patented in the US, unlike Europe, where code is considered mathematics and hence not patentable. Hence, neither are the results.
From the lookalike versions of Linux for OS-X and Windows, I assume there is nothing to prevent this, unlike the inclusion of certain items of code (eg codecs) in some territories like the US and Japan.
If using Apple , Adobe or MS screen shots in a publication that I intended to make money from, I would clear it with each company, making clear which territories were covered. It might also be worth asking the FSF or similar organisation for their view.