This isn't the case on my phone. I have been playing with these today (and with your useful tvcatchup script!) and I have found that a reboot is required after editing /usr/share/applications/defaults.list and not after editing /etc/gnome/defaults.list. I suspect perhaps that /usr/share/applications/defaults.list is used to populate /etc/gnome/defaults.list at startup but not really sure. Cheers, Jan
~ $ ls -l /usr/share/applications/defaults.list lrwxrwxrwx 1 root root 24 May 18 10:50 /usr/share/applications/defaults.list -> /etc/gnome/defaults.list