Publishers have to find new ways to add value, or to justify the percentage they take from authors. Or perhaps alter the percentages. Authors are now free to publish their own works, and some are making a damn good living at it (Joe Konrath looks to bring in well north of $500,000 this year... I'd call that pretty damn good). Yes, that means authors have to deal with finding someone to edit their books, format them, create a cover, write blurb copy, upload the book to all the different services, create and execute a marketing plan, and spend a lot of time marketing their books and keeping track of all the details of accounting and the various fiddly things to deal with the online book publishers like Amazon and Lulu and Smashwords and others.
Some authors are capable of dealing with some or all of that easily. Some don't want to deal with any of it. Services exist to provide all of those things for a flat rate, so authors can line up any of those things they don't want to deal with directly. (Which still means selecting a vendor and managing them, which some authors don't seem comfortable with doing.) When an author can do it all themselves, and reap a 70% royalty instead of about 10%, publishers now have to show why their much lower royalty rates are in fact a good deal for the authors.
I don't think any publishers will really be able to do that. Publishers will have to boost their royalty rates (on e-books at least) and change many of the annoying things about their business (like taking 18 months from getting a manuscript to release of a book) in order to get authors to sign with them.
Really, what ebooks and digital distribution have done is expose all the weaknesses of the old publishing model. The whole concept that more than half of all the books printed end up getting returned and pulped shows massive inefficiency. Which leaves room for a much more efficient model to transform the industry, which is occurring right now.
E-readers will only get cheaper, better, and more prevalent. As tablet computing spreads with amazing speed (1 billion tablets by 2014), ebooks will become the main source of book revenue. Specialty books, such as fine editions of novels or art books for the coffee table, will continue on. But mass-market paperbacks will never again hold the prevalence they have in the past.
Will there be a lot of crap? Oh, yeah. But the good stuff will find an audience. Marketing will be important, but I think it's more about getting your good work known more quickly than it would without marketing. If you write a really great novel, people will find it and talk about it and it'll get known eventually. Marketing won't magically transform hackwork into brilliance; what good marketing will do is help your work reach its market potential more swiftly.