Sorry I'm coming late to this original discussion.
As one of the publishers involved in the original question that started this thread, allow me to add my two cents . . .
It is very typical in the publishing community to not allow "simultaneous submissions" so as to avoid the very issue of simultaneous publication. This is entirely a publisher's decision. In our case, we buck the trend and specifically do no prohibit it. We do so for the simple reason that we often hold on to an accepted submission for some time before find a place to publish it -- space being a very limiting factor for us. We feel it would be too restrictive to prohibit a photographer from sending their work to anyone else while we are sitting on it. So, that's our policy.
Having said that, we do feel it is best, when possible, to spread the publicity around as much as we can. We try to avoid simultaneous publication and often ask the photographers we're scheduling if there are any other publications that might be using their work in the near future. Sometimes the photographer doesn't know -- they've sent in work and it just appears by surprise in some publication. Sometimes they know it will be published, but have no idea when. If they do know they will be appearing in another publication and when, we try to schedule them in LensWork so as to avoid a simultaneous publication, if we can.
Occasionally, however, this becomes unavoidable. For example, photographers are looking for as much publicity as they can when their new book is being released. Nick Brandt's work in LensWork #61 is a case in point. Sometimes (and this is the case with Alan Ross) we are caught by surprise when there is a coincidental simultaneous publication.
But, even when this does happen, it is usually quite interesting to see the difference in editorial approach. We rarely see the same portfolios, although it is not uncommon for at least a couple of the images to be the same. It is interesting to see how different magazines choose to layout the same work. Printing differences become readily apparent in direct side-by-side comparisons. The number of images are typically different. Obviously, the content of the article/interview is different. Personally, I think a simultaneous publication can be a very useful way to learn more about a photographer and their work -- a sort of examination from different angles that adds to my understanding of that photographer.
LensWork (in print) has always had just 18 slots per year, three portfolios per issue (we are increasing this in September with LensWork #66 to four portfolios per issue). Now with LensWork EXTENDED, we can do a lot more than that (LXT#65 has 9 portfolios, for example). Statistically, simultaneous publication might increase as we publish more and more photographers -- unless, that is, we get more and more quality submissions! (Hint, hint. Never forget that publishers are always on the lookout for content -- when was the last time you sent in work to a magazine for consideration?)
Finally -- and I hope this doesn't sound too self-serving -- I like to think that LensWork is different than other publications. I've always thought of our portfolios as "little books-within-a-book". As many of you know, the first 12 issues of LensWork didn't have any images at all. We just didn't want to be another "my greatest hits" publisher. Then I realized that in every workshop I'd ever attended there was always a photographer who'd show a portfolio, that is, a body of work that was intended to be seen as a group -- 10, 12, or sometimes as many as 20 images that explored a theme. This was usually not used as wall-art because it needed to be seen as a group. Nor is this enough content to be a book, so publication was out of the question. Galleries typically avoid portfolios because they want your "greatest hits" so they can sell as much as possible. So, where do these portfolios go to be seen? Nowhere, or workshops at best. With this realization, we decided that this was what LensWork could bring to photography that other venues did not. So, in 1996 we started publishing these little books-within-a-book so portfolio projects could have a place to be seen. To this day, this is still our approach. Remember those thin little books that we used to get each quarter from the Friend of Photography? Marry that idea with the portfolio and you get LensWork.
Brooks Jensen
Editor, LensWork Publishing