I believe GPL means that any source code that is borrowed from another source under GPL must be made available as well. https://www.gnu.org/licenses/gpl-faq.html#WhyUseGPL

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"Does the GPL require that source code of modified versions be posted to the public? (#GPLRequireSourcePostedPublic)
The GPL does not require you to release your modified version, or any part of it. You are free to make modifications and use them privately, without ever releasing them. This applies to organizations (including companies), too; an organization can make a modified version and use it internally without ever releasing it outside the organization.

But if you release the modified version to the public in some way, the GPL requires you to make the modified source code available to the program's users, under the GPL.

Thus, the GPL gives permission to release the modified program in certain ways, and not in other ways; but the decision of whether to release it is up to you."
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Personally, I use both linux and windows miners and have used both lolminer and optiminer. Aside from this post, I'm not getting into this drama and appreciate the work of both miners, however, it does seem those demanding a Windows miner are lazy. Linux distributions are generally free and running a miner on them is not too difficult at all (though more involved), especially with many tutorials available or bitcointalkers willing to assist. Just create a dual boot disk and you're good to go.