I think, giving Canon the benefit of the doubt, they were cautious and they didn't bother testing the multitude of legacy products for exact specs. Of course this works both ways, it "encourages" people to buy newer bodies, but on the flip side more accurate info might have encouraged more 600 sales to older camera owners who don't intend upgrading bodies but do want better flashes.
For instance, the specs say my sync speed goes down one stop in RT mode. I have found this is not actually true most of the time, but is sometimes, that is, I sometimes get a shutter shadow at 1/250 but most of the time don't. I haven't pinned down what, exactly, is the setup that does get the shadow but I well understand Canon just saying "you lose one stop of sync speed in RT mode"
rather than going into every combination of every camera, can you imagine the outcry if they didn't put that proviso in there and people called them out on it?
What I was hoping for prior to purchasing my RT system, was actual user feedback on their own real world results, I never could find it though which seemed strange bearing in mind all the people here who listed owning 1Ds MkIII's and 600EX-RT's, yet not one of them, even via PM, could give me any heads up at all.