/etc/xdg/midori/config sets homepage=file:///usr/share/ubuntu-artwork/home/index.html which isn't present in derivatives

/etc/xdg/midori/config contains:

 [settings]
 homepage=file:///usr/share/ubuntu-artwork/home/index.html

which naturally isn't present in derivatives, and so in for example Kubuntu (and presumably any derivative distribution that doesn't unclude the ubuntu-artwork package) you get an ugly "Error opening file: No such file or directory" as your default homepage.

Looking at the dependencies, merely making ubuntu-artwork a dependency of midori wouldn't be good, since it pulls in a bunch of cruft that folks running other desktops wouldn't need namely a bevy of GTK theme packages). But looking upstream, Debian defaults to

 homepage=file:///usr/share/doc/midori/faq.html

which is in fact installed by the midori package in the Ubuntu repos, and so seems like an entirely reasonable, DE-agnostic choice.