Alternately, it could imply that the repository, or an individual application "update feed", gets installed along with the app. Further, I could imagine that what the site is actually proffering is a shell script that simply adds a repo repository and then calls apt.
Having checked: Clicking the "Install" button for the "RAR" app redirects to "apt:rar?section=multiverse", which, I imagine (not having Linux installed, I can't follow further) opens in Synaptic. Looking around, I can't find a link that doesn't point to either the default, universe, or multiverse repo, so I assume it just doesn't offer externals.
"Install" button on Chrome/Ubuntu runs xdg-open apt:<package> that on Ubuntu 10.10 opens Ubuntu Software Center.
The homepage is not so updated, it does not mention the last Ubuntu version.
I don't see who that site can be useful to.
What would be good is if it can add the repositories to the sources.list so that upgrades would also be taken care of. I dont know if this is done already.
If the above is already done, a country specific repository list would be even better.
So does this imply that there are no software upgrades (including security upgrades) if I install something not in my repositories?