Jacket Whys: Swirls and Light

We found recent commentary about the "ever-growing trend toward the exclusive use of photo-shopped images on kids’ book covers." The author cites four examples, including Brad Strickland's Grimoire: Tracked by Terror (2007):

...the inner-lit red book against a green background is the focus, so are we drawn to the boy’s face by the circle of blue-green light that just happens to surround his head like a halo.

Will we see the end of illustrated book covers for children? How much cheaper is it, in the end, to use stock photography? And are these kinds of covers only effective with younger kids?