Different printing setting in Gnome Shell and in Unity

You're actually looking at two separate applications. The screenshot at the top is system-config-printer (called "Printing" in the shell) and the screenshot at the bottom is gnome-printers-panel (called "Printers" -- but they may have the same name in your language!). Both are available in both desktop environments.

The latter one is probably supposed to replace the former in Gnome 3, but as you have noticed, it isn't as functional as the old one (yet). That explains why both are installed.

I can't explain why printing doesn't work in Gnome Shell. Do you still experience problems if you use system-config-printer to set up your printer in Gnome Shell?

A nice way to get around this is to make the old printer settings launcher visible in Gnome Shell is to edit the launcher directly:

sudo nano /usr/share/applications/system-config-printer.desktop

and change the line NotShowIn=KDE;Gnome; to NotShowIn=KDE;.

Also, as Timo mentioned above, the name of the new and the old printer settings launchers may be the same, so you may also want to change the line Name=Printers to something like Name=Advanced Printer Settings.