I can totally see where Scott is coming from on this one, and predictably there is outrage from people at his viewpoint either by taking it literally or finding a very specific situation in which having a photograph of a cat is essential.
Firstly Scott Kelby does do Photoshop tuition, but he also is a photographer, runs web-based TV shows on photography and is great friends with many exceptional photographers - including Joe McNally who might be a more recognisable name for some people what with 30 years at Time Magazine and National Geographic. He might well be doing this to stir debate, and drive people to his site & services - but I also think he makes a great and valid point.
1) He isn't saying that specialist pet photographers, garden photographers, or even high school senior photographers (see person on railway track) shouldn't have relevant galleries of images to show in their portfolio.
2) Certainly if you were making a targeted approach to Airfix you would want some relevant model aircraft and/or small toy products to show (although I'm not sure what the market is for Airfix photography ;-) )
Scott's point is that with the vast number of full-time professional, part-time professional, and prospective professionals all looking for customers, and all competing with an even larger number of very-happy-as we-are-enthusiastic/advanced-amateurs (who by the way produce increasingly excellent work) that it is very very hard to get noticed. Very hard to differentiate yourself from the mass-market magazine reading hobbyists, and they will probably have seen 20-30 similar sets of images that week.
Create a gallery of a photo of a flower with a bee, a sunset, a railway track, a racing car, a mobile phone, and wedding group image taken from the side, a photo of one of your kids and then try to market yourself via a click-pic/Weebly website or Facebook page and you'll disappear into the mass of mediocrity because everyone else with a camera can do exactly the same thing. Even if you took technically correct and compositionally well thought out versions of them.
Build a documentary / photo-journalism website to showcase your skills as a news photographer with a series of images of the homeless in a particular area telling a comprehensive story and you might hook the attention of a charity or a magazine/paper. Because a single snap of a homeless guy on the street as you walk past them is "easy" to achieve - spending the time doing that story well over 20-40 different images isn't at all.