Over here there are basically two types of rear racks and they can be seen at the following links ...

tubus - Cargo classic

tubus - Logo classic

The Ortlieb bags I use can only be used on the second type of rear rack which has an additional set of rails that position the bike bags a little further away from the bike itself.

Almost everyone over here (excluding racing bikes) uses rear racks and the majority of folks use bike bags as well.