The answers you have gotten don't really give the repository system the credit it needs, IMO. A repository alone may be a glorified FTP server, but combined with other elements of package handling it's way more. In my opinion package handling is one area where linux is far ahead the more popular OSes -- this is also why many people do not understand it: they're used to an inferior system...

Repositories (the servers with installable packages), and the package manager (called Application Manager in the tablets) enable these things:

• easy installation (no more searching for software on seedy corners of the web)
• security (software comes from fewer sources so it's easier to make sure the sources are trustworthy)
• easy upgrades (you don't have to check if a new version is available, the package manager will let you know -- and this covers all installed applications)
• more security (developers can push security fixes out quickly)
• more easiness (just one UI for installing and removing things)

In the future the whole OS may be upgradable to the next version using the package manager (this is what normal linux distros do already).