Rockwell seems to think that art is above commerce, fine for an artist, silly for a commercial photographer who's trying to put food on the table. You get hired by knowing what sells, not by having an inner vision of the world that you translate to film or file.
Rockwell's idea of a "whore" is your aspiring fashion photo student's ideal of a "style". By your style shall you be hired.
One strange genre that he missed was the "professional who assumes they're an artist" those photographers who confuse money with vision, as in "that's a professional image". Rockwell rightly defines professional as "making money" and doesn't confuse the definition with any influence of "professional workmanship" equated to "art".