Indeed, there isn't one: no-ones been uploading their content to the systems currently available. Having said that, I can see a clear distinction between application software (which may be supported by the author, has distinct versions etc) and user-generated content such as background images.

Themes are effectively applications, so should be in downloads.maemo.org, as could userstyles (and, if desired, backgrounds or - more likely - collections thereof).

Flash games are a little dangerous: copyright violations are likely to be occurring left, right and centre if they're uploaded to random places.

All of your examples could fit into downloads.maemo.org without requiring too much in the way of a user contortion.