A pacman -Syu will do the same as a pacman -Syuw when it can't download all packages ;). However, a user perhaps wants to update a few packages that are important for development or regarding security issues and might try to update other packages some days later, then Syu(w) isn't an option.
You are _not_ supposed to do partial upgrades! Archlinux does _not_ support that!!! Whenever you do a sync (-Sy) you have (!!!) to update the whole system. So either -S to install or -Syu to update! Doing anything else should not be advocated. Some people on the irc would go furious if they find about that! Download all packages then install them. I wonder where in Germany you are that you don't have a good connection.... It might be slow, but you should have internet basically all the time....