Maybe I am always getting the wrong impression - but (in this, as well as it seems, many other posts on almost all forums when this issue arises) there seems to be an anti-gallery or sour grapes flavor to most responses. A gallerys primary purpose is to sell the work on their walls and turn a profit. Why? So they can keep their doors open to make more work available for sale, etc., etc., etc.
Anyone that has mounted and "properly promoted" an exhibition knows the cost. If not, then maybe they should budget one out to gain an understanding of what is involved. A gallery that believes in your work and is willing to agressively represent the work makes an investment in time, resourses and $'s before and after the work is shown. The mistake many photographers make (as was mentioned) is thinking that all gallerys are the same and follow the same procedures. A "good" gallery knows their market. They know who buys the type of work they choose to show and why. Its the reason some of them might insist on limited editions and others could care less. Gallerys that do not understand their clients dont last very long.
The next time you go to an opening at a well run gallery (successful) realize that the owners are happy that you came and added to the numbers of warm bodies, but the people that they are most happy to see are those people that are there to buy and it was the reason they were invited. And I have yet to hear a photographer complain when a gallery has managed to sell their work for top dollar and create continued interest in their work.
A museums job is to show work - a gallerys job to sell work.