@togath: It’s the usual shell behaviour: if a string doesn’t contain characters that are considered as separators (like spaces or operators), the quotes can be omitted. If you use the quotes everywhere, you are on the safe side.
@Ohmega: /etc/network is a generalized configuration file. Some packages (e.g. the network backends) contain scripts, that convert the information from /etc/network into formats understood by these packages and/or create other system-wide configuration files from it. This allows us to switch network components without having to adapt the XBMC/Kodi network configuration addon. As for bftpd: It looks like this package is not honouring /etc/network :(.