A bootable .iso is a bootable .iso the tool used to burn it to the disk does not make it bootable that is already present in the image itself it only needs to be burned as image to the disk not as a single file to get it right. Oh and it is not a MS tool they ripped off open source program for it.
http://arstechnica.com/information-technology/2009/12/microsoft-finally-open-sources-windows-7-tool/
And a non-bootable ISO is a non-bootable ISO but Microsoft's tool WILL MAKE it bootable because it will grab the necessary boot files from the working PC.
Windows installers came in many different flavors and some were meant to be run as executables on an already booted PC.
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