If you could get the Windows source code with some paid subscription program, so that it's not pirated, it still wouldn't be open source. It would be more like "open access".
Open source means we can modify it and share our modified version, and even charge for it.
Most users of scientific papers aren't looking to extend those papers and redistribute modified copies; they just read them privately and make citations (which nobody can tell whether they were from a licensed or pirated copy).