Numbers is not installed as part of the operating system build. It is a layered application that the newly purchased Mac would have installed by Apple as a courtesy app, and it certainly can be removed from the Application folder.
Numbers is not automatically updated by an operating system update or upgrade, and would need to be manually updated via the Mac App Store Update panel if it appears there when a new version is released, or directly from its Mac App Store page as a download.
If the installed version of Numbers is incapable of accessing documents created by the current version of Numbers sent my someone else, then one's only recourse is to use Numbers for iCloud to get around that issue, and a network connection certainly would be required.