If the argument is that limiting the edition will enhance the value of the prints, then what earthly argument can be made that issuing in another size won't decrease the value of existing prints. A similar argument can be made about issuing follow up editions in platinum or gravure which has become popular lately. This comes into play in historical etchings and engravings as well as in modern prints. The objects were sold as works of art and the limiting factor was the plate and the printing process itself and how many images could be pulled without serious degradation of the image. It is suspected that early pulls off the plate made by the artist to get a sense of the image as it was being developed, found their way into the commerce of the print market.
Modern printmakers are occassionaly known to rework plates.
In fact if stock brokers were to behave this way, there would be a lot more of them in jail. Photographers and galleries could in fact issue a disclosure statement to the buyer that this image is only limited in this size, and in this medium, and that any number of future prints could be made in other sizes and media. I am sure that not too many galleries of photographers would be willing to do this. As a buyer I would see this disclosure as an admission that the edition, is in fact, not limited.