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I think it's a mistake to read too much into the reality vs. raw argument. I don't know first hand, but I suspect, that freelancers where getting a little too comfortable with all the sliders in Lightroom and were delivering over-processed images with vignettes, heavy shadows and HRD-ish shadow recovery too frequently. The editors at Reuters are certainly aware that in-camera jpegs aren't a perfect rendition of reality, but this policy will probably make their lives a lot easier without costing too much in terms of image quality.
While in-camera JPEGs certainly are "developed raw files", they are developed by a (limited) set of generic algorithms, developed by some one independent of the photographer. Thus, they have no motivation to (willfully) alter the newsworthy content of an image, or the knowledge about what is newsworthy. They may well do things to sharpening and contrast and green hue/saturation that corresponds with how their study-groups preferred their raw files developed, but I think those things are less critical for a news agency than e.g. removing people from an image.
I agree that Reuters probably are doing this to make it "a little harder to cheat", and/or to ensure that those who "cheat" are really motivated and cannot possibly defend themselves if and when they get caught.
I believe that Lightroom makes a list of edits in its exported jpegs. It would be interesting if raw developers offered a legally/technically 99.x% believable signal chain. If you used your camera with signed raws, imported those raws into a raw developers and made some edits, the exported file could include some kind of "certificate" authenticating what it was and what was done. Perhaps this would be easier for camera developers to do (since they own the camera hardware). Then photo contests, news agencies and courtrooms could apply whatever regime they desire.
My understanding of courts is that an image has to be "an original" in order to be presented as evidence, and that it cannot be lossy compressed? If so, I find it amusing that the (quite heavy) processing done in (automatic, proprietary) raw development is of no interest. One might think that images presented in court should be processed by open-source raw development software so that the algorithms are free for anyone to find bugs and artifacts.
-h