The "source" file for the update will be different sizes depending on whether it is .cab, .msu, or whatever. The "source" files are just a distribution container, the files inside that container are the same. If you were distributing a DVD full of updates, then I think your understanding would be correct. But if I understand the process correctly, once you have installed/integrated that update into your updated AIO OS build, then those updates are all expanded/stripped out of their containers and either replace existing files or are stored in a "install pending" location. In either case, I believe that the format used inside the OS to store those files is independent of the format of the "source" file. I could be wrong, but that is the way I understand it.
sigbin reacted to Legolash2o in What are GDR, LDR and QFE Updates?