Well, my take on it is that someone operating on a high professional level has learned from his experience to nail the exposure and White Balance and, assuming the scene is in a manageable lighting environment, really wouldn't benefit from shooting Raw -- a wedding shooter isn't going to need to keep all those Raw files and "masage" them for creative output (although those that have special post processing "styles" may or may not benefit).
Now, shooting say a reception (or ceremony) outside on a sunny day may give one pause because the highlights and shadows become challenging and you can't do much about rescuing them with jpegs. So there is where I'd think a pro would make a choice, again based on experience, as to whether he can capture what he needs in a jpeg, or use a flash, or may choose to shoot Raw.
A lot of studio people shoot jpeg for the same reasons -- they have control over the lighting and have the experience/skills to nail the lighting, exposure and WB, and for their workflow they can get good results and deliver the results and don't need the "baggage" that Raw could bring into the work they do.
Just bear in mind that these people are working, producing a product, not out to enjoy a hobby or fine art/landscape/scenic photography with the goal of creatively drawing as much "cool stuff" out of the image as possible.