Dead horse ahead alert...
Actually it all boils down to what is one's definition of "full frame".
If your definition is "full frame = 35mm film size" then yes, 4/3 and APS-C are all "cropped" sensors and medium/large format are "multiplied/humongous" sensors.
If your definition is "full frame = capture full image circle projected by lens" then 4/3, medium, large format etc. are all "full frame". And APS-C bodies using lenses designed for APS-C is also "full frame" (e.g. DX bodies with DX lenses). You only get "cropped" if you are using smaller sensor which can only capture a crop of the image circle projected by the lens (e.g. DX body with FX lens).
The argument about multiplication vs crop factor also depends on one's personal definition. If your sensor captured the full image circle projected by the lens, where's the crop? Hence Olympus users prefer the use of "multiplication factor" when comparing FOV to the more common 35mm size. Otherwise it'll be like saying medium is a 0.5x "crop" factor when there is no "cropping" involved. So to us, APS-C sensor + APS-C lenses -> multiplication factor. APS-C sensor + lenses designed for 35mm film size -> crop factor.
Peace out guys...