My impression (from waaaaay out here at roads end on the northwestern edge of the continent...and remember, that letter was written 5 years ago) is that there are some gallery owners who bellied up to the trough to get rich, and some collectors who only buy photographs to add to their investment portfolio. Neither has the long term welfare of the photographer in mind, except in somehow increasing the purchase price of the photographs. My point was that the Internet allows photographers another way to sell their work without having to play the game by their rules.
The trick is, a) how to get people to discover your photography, b) how to get people to realize the worth of your photographs without a gallery holding peoples hands, or without giving your work a 'stamp of approval', and c) what kind of pricing structure will work for you and your images.
Part of the problem of people purchasing from a photographers website (particularly for large images) which is also true of eBay is that the viewer can not truly see the quality, the tones, color, exposure, etc of the final photo. These can only be seen in person. That is why I have observed over the years that purchasers of my work usually have seen the work in person (as in from Art Shows), but they may purchase the size based upon their available space which they can later confirm on the website.
I don't know if Cole did this or not. But Kim did a number of photographs where he made one print from the negative and then he taped it to the back of the print for sale. In an interview he did within the last two years, he stated that he did this as a way to "let go" of the negatives, a stage he had to go through. Certainly each print was unique. He no longer does this.
A number of prints by Kim with the negative attached to the back can be found at the above link.