Okay, I waited for a time-out again and the Nokia Applications and Nokia System Software Updates catalogues both give the error:

https://downloads.maemo.nokia.com/fr...mr0/./Packages
Resolving host timed out: downloads.maemo.nokia.com

Here's something interesting though, if I disable those two catalogues and enable Maemo Extras (which is at http://repository.maemo.org/extras/), it updates through wi-fi without any problems.

So the downloads.maemo.nokia.com catalogues cannot update through wi-fi, but the repository.maemo.org catalogue can.