His conclusion is not really a function of the file format -- it's everything else!
I've seen tests that suggest the Fuji sensor has a slight tonal range advantage. More latitude allows for less precision in the capture; you can "nail" more shots exposure-wise. That's important in an environment like wedding photography, where a lot of your work is shooting candids in a changing environment.
If you shoot the exact same scene (cropped in the viewfinders to match) with a small-sensor camera (like the S5) and a full frame camera , the small sensor will have a greater depth of field and therefore, when the subject has depth, the small sensor camera results in a sharper image. This too is important when you're shooting things like groups of people.
These are just two ways the physical aspects of the camera sensor could result in an improved image (assuming you want more sharpness and latitude). Neither has a thing to do with the RAW file format -- but you'd see the difference in using the RAW files.
But then, I think you're right Jonesey --I want to feel good about what I've bought too!