Yes and no. Format does affect content (and style).
And it affects writing style too. Jean Baudrillard wrote a lot on this, exaggerating sometimes, but I have found out from experimenting how much of it is true. He made the difference between writing on a typewriter and writing on a word-processing program, and how much the computer actually does for you. This is definitely true, because it allows you to speed, easily correct and then think that the same 'content' came out anyway. When I'm trying to write something that's going to last instead of evaporate, I even write it all out in handwriting, which is even less mechanically mediated than an old kind of typewriter. I only write first on the computer if I am sure it doesn't radically alter what I'm working toward, i.e., the removal of aspects of labour from something can affect the tempo and tone of something.
We are far too early into what may be the era of the e-book (I think that announcements of the demise of the old kind of book are still premature) to tell, but it’s possible that writers may write differently as and if the reading styles of the audience changes. Would this be as radical a change as the one after pre-printing press era, when poems and stories largely ceased to be heard in groups by a live audience and began to be read on the page by one solitary reader? Maybe not, but that doesn’t mean there won’t be significant differences, as time goes by, in reading from the printed page and reading from screens.
I think it's premature in the sense that the predictions are probably off, but not wrong. And I definitely think we already see much fiction, yes, even between hard book covers, that reflects the influence of cyberspace and a certain hyped-up sensation that goes with it. You can even find it in fine writers like Salman Rushdie. The difference in P.L.U. (People Like Us...that is, at Ballet Talk) as opposed to cyber-sites that are not steeped deeply in tradition, is that there is much less continuity, threads are rarely renewed, and there is a greater interest in the cyber-aspect of the discussion much of the time than there is in sites which are extensions from arts like ballet, opera, classical music, theater and even film by comparison. The contributors become much more like characters of some kind of cyber-punk fiction in the younger type of site than they ever do here. It's impossible to do that here, which is wonderful relief, but this is an example that is the same as Carbro reading 'Great Expectations' in whatever format. First, we are talking about someone, and many others here, who are familiar not only with fabulous live performances of all kinds, but also books that are not only physical, but even have illustrations on their old pages sometimes. That this kind of touch gets you closer to the original is indisputable, I think. But that person who is steeped in the tradition is not going to get infected with an addiction to e-books the way a teenager who spends hours a day 'friending' on MySpace, so that it would be according to the person whether 'Great Expectations' really stays 'Great Expectations' or is just another piece of screen flotsam.
The real issue in the future of e-books is very simple, being purely economic. If it becomes prohibitive to continue to afford books, and free to read them online, that plus the fact that sales of print publications is down and when a publisher is sold now, they are considered incredibly lucky. I'll look this up to get the exact facts. At any rate, it will be something to do with economic factors that determines whether the changeover into many online things affects some things more than others. If it is a radical change, no matter when, I would think it would definitely be an evolution into something as singular as dirac's example of moving from the oral tradition and other aspects of the pre-printing press world. Many people still choose to read a physical newspaper, but they don't have to. At this point, they still cannot choose to eat off a screen, which may explain why restaurants and cuisine are at least one of the arts which seem to be at their highest degree of refinement right now, and other arts seem to be floundering--reproductions will do for many people.
Edited to add: still searching about that big publisher sale in the last 2 years, but there's a lot on the web about the decline of print culture. Actually, Conde Nast appears to be doing well, I'm still searching....