Mainly the first one; being able to use Steam's networking library, which as you say has the major benefit of not needing to know the first thing about stuff like routers or Hamachi.
It's a bit of a shame that a decent chunk of players can't enjoy one of the main features of the game just because they have a shoddy router or silly ISP!
The old networking system will remain in place, of course, for DRM-haters (and pirates) ;D