Comment # 6 on bug 950996 from Michal Filka

There are several ways and reasons how/why to configure network even before
starting the installer. These ways are manual (via linuxrc) or automatic
(linuxrc even yast, but at the very beginning of installation). Network
configuration dialog in installer is intended mainly as a backup when automatic
way is unable to configure the network properly.

Also network configuration of installed system can be very complex (bonding,
bridges, vlans, tunnels, ...) and it usually don't make sense to have
such/whole complex configuration in installer. Note, that yast doesn't modify
network configuration of target system when upgrading.