Microsoft hasn't exactly been sue-happy over update files AFAIK. Someone here can let me know though. There might be an issue with using the "Windows Update" branding though.
FWIW, there's also Legacy Update which does a similar thing for Windows 2000 and newer.
Fellow Endeavour user here (with KDE)! Arch is nice, but after installing it so many times it's just nicer to have something set up for you.