Corporate X, catalog X, products X, advertising X, technical, medical, research, legal X, etc.[/QUOTE]
Not to sound like a phallus, but I know weekend warriors photographing for money in the above fields with a red "X" after them.
There will always be some in just about any field of photography. There are dozens of stories of some amateur somewhere that landed a very high paying advertising gig because they did something very unique and different that caught the attention of some creative somewhere. But at that level, its rare to have any competition from amateurs. And at the lower end, there are many small businesses and corporations that look to the amateurs to fill image needs.
But in the middle, from my chair it's mostly professionals competing with professionals. I shoot mostly corporate marketing and advertising, and I rarely run into competition from amateurs when bidding. I know quite of few of my peers, and rarely do they complain about loosing work to amateurs. This is in stark contrast to those shooting wedding, sports, portrait, concerts, theater, etc, which many are voicing their concerns.
All I was pointing out is that the competition from amateurs is eased when shooting for projects higher up in the food chain, and in areas of photography where the barriers are higher. I.e., requirements to put up 5K to produce a shoot and waiting for months to recover that in billing puts off many people (do a few of these a quarter, and you could be out $20-25K waiting for invoices to be paid). Submitting bids that are missing critical items signals to clients they might not have the experience needed to produce their project, and thus being passed over by client. The need to be available during business hours for creative meetings, etc. The need a producer, well trained crew, freelancers and adherence to employment laws. Liability and errors and omissions insurance required by contracts. Even having a good understanding of basic commercial contracts and bids eludes many amateurs. Things like these weed out many amateurs, not all, but enough to really ease the issue with competition from amateurs the higher up the ladder you go.
The more barriers that are in the way, the more amateurs and hobbyists that drop out. The higher up you go in those fields, the more barriers there are. All of these can be used to an advantage for photographers that find and conquer these barriers, as it brings them higher up the ladder where fewer amateurs are competing. The amateur and professional may have the same photography skills, but the photographers that have conquered these barriers will be further up the ladder with less competition from amateurs that haven't.
Add creativity, providing excellent service, and finding your own niche in the industry, and it can be very viable. Jumping in the areas that are most crowded with competition, amateur or professional, or worse both, and things look much more bleak.
I have yet to land a $100K to $250K day rate job like those few we hear about every so often

I don't think they are too worried about the hobbyists and amateurs! And there is a lot of ground between the two extremes.