You are right about the 1200 GS not having a separate filter, but it has filter media as part of the fuel pump (some will dispute this, saying it has nothing, but you need to look at expanded schematics of the pump to see it). In order to make the pump last, it has a mode to make the pump run at 70% capacity when full flow is not required. I've heard that a 1200 GS injector is pretty large and that it will pass some stuff (fine sludge, etc) without a problem. I've not seen this and cannot confirm the accuracy of this statement.
KTM 690 R - "Its just a little crush..."