If you have downloaded Mavericks once, then you can create a bootable USB from the installer:
Run this before you install Mavericks on the machine you downloaded it from, otherwise you won't be able to find the installer in your apps folder:
Create Mavericks Boot USB
sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ Mavericks.app —nointeraction
The USB is named "untitled" in this example. If your USB is named differently, then please change the command above accordingly.
Thanks Petvas for your answer - that was very useful information and I will save it for future reference. However it does not answer my question above.
I am wondering whether it will be possible to download various future update installers for archival now that Software Update has moved to the App Store.