Have you seen the source code for what you download from Technet?
No, but You also did not manually inspect your favorite Linux source code line-by-line to see if it contains backdoors and you cannot be sure that the ISO images You used are compiled from these sources, right? The patch files contain files and instructions that can be unpacked and inspected (at least what files are replaced etc.).
If the answer is no then you a trusting Microsoft.
I'm fully aware of this problem.
Unless one does not update Windows at all there is no getting around the trust of a single centralized authority controlling over 90% of computers worldwide.
Not updating is bad idea, just as bad as allowing the Windows Update to install whatever Microsoft pushes on Windows update. At least I inspect every patch before I put them on my production computers.
The key difference is that with Free Libre Open Source is that the source code is there for everyone to see. If a GNU/Linux distributer were to distribute binaries that did not match the source code they would be exposed in no time and in addition would be liable to civil and criminal liability for copyright infringement. So I do not need to inspect every line of code to not trust the GNU/Linux distributer and yet use that distribution.
But even if the network suffers attack from Microsoft that disables 60% of nodes, the network will continue to function. Yes it is true that FPGA and ASIC must be controlled by computer, but many miners use other OS than Windows. There is less Bitcoin users that run Windows than in general population. Microsoft using such method will be like a Derp Gun - single shot, high damage, low accuracy and years long reload time.
Of course the fact many Bitcoin users do not run Windows is a great source of strength for the bitcoin network.
More danger will come from making Bitcoin illegal like P2P file sharing is. The Bitcoin is not encrypted or obfuscated and users who are running nodes in plain can be harassed by law enforcement like torrent uploaders are right now.
P2P file sharing is
not illegal. Copyright infringement may be illegal under certain circumstances; however the most common liability for individuals is civil damages. In the scenario where a government were to try to stop Bitcoin the most efficient method would be to get Microsoft and Apple to shutdown most of the nodes. They can then concentrate their resources on the much fewer remaining GNU/Linux nodes. What is is really scary is that this can be done
without making Bitcoin illegal thereby avoiding the legal and constitutional challenges that would arise in many countries. The best analogy is Wikileaks, just replace VISA, MasterCard, PayPal etc. with Microsoft and Apple in the Bitcoin case.