<rant>
There is a file format which will add a repo - the .install file format is well-documented in the Application Manager documentation and "how to build a deb file for Maemo".

TBH, most of the problems with Maemo application installation is entirely due to packager laziness: all apps should (once stable) go in the "Extras" repo. It's not helped that many apps seem to be depending on libraries in other repositories, without documenting what those are! ("Oh, you mean you don't have repository.maemo.org configured? I do, and I use libxyz from there")

As for preferring to download packages - this is just plain backwards: you end up having to track down all the dependencies yourself, with no real idea if they're already installed or not. Repositories and the Application Manager are the way forward, but authors should stop creating their own repos!
</rant>