Apps in testing should be complete. They're just waiting until enough people have tested and approved them (and for the minimum time period to pass) before moving up to the main maemo.org repository. There's now a dedicated testing squad working to get the current backlog cleared and make sure apps move one way or the other out of testing as quickly as possible.

For apps in devel, it's entirely up to the developer/maintainer. Some of the apps have absolutely no chance of passing testing (because of how they've had to be implemented, or because of what they do), so they'll never leave the devel repository (they can still be very useful for those who need them and know the issues/side-effects). Others are still undergoing heavy development, with a small number of users providing suggestions/requests to the developer. Once the developer is happy that the app is sufficiently developed to have a wider release, they'll push it to testing. Yet others are dead, with no sign of any ongoing development work - they may get picked up again in future, or may eventually get cleared out (not sure whether there's any system in place for that though).