[Krazykiwi]

I have to agree with Cinisajoy on the static vs changing.

I buy books (e or not, realise they are books to most people) for:
a) Novels I want to read. Probably once, maybe more.
b) Reference material and textbooks that are not freely available on the web, and are static.

Portability has nothing to do with it for me. I live in Europe, if i have something to read an ebook on, I have free 3G and probably wi-fi so I could just look at a website.

I am not interested in an ebook that is constantly updated, because it's pointless to me - that's what websites are for. I can't easily cite a book in a standard format that isn't static unless it's got very clear edition information. Citation formats simply point to a website per a specific date. Citing books don't, reference material I can't actually reference in a manner other people can look up, is not useful to me. The Wayback machine, for instance, lets people look up an older version of a website, or I can snapshot it. A ebook, on the other hand, will likely have only the current version available, and no way for others to look at what it said in the specific edition I cited.

(ETA: You mention ISBN's giving some kind of impressiveness? Realise, if you make each new update a new edition, you'll have to give it a new ISBN, if you are in fact using ISBN's. Amazon allows new editions without changing the ASIN, but they don't use ISBN's for ebooks anyway. An ISBN doesn't mean anything, it's an identifier for distributors, and a way to differentiate editions, it's not a stamp of approval in any way.)

Further, very few readers are set up to deal with books being updated, because... books don't get updated much. Kindle can push them out, but it's opt in, and unreliable. It's not the expected use case, so the infrastructure is not there for readers. I don't know of any other stores that even has the possibility (and I have books from several). This is probably the biggest problem, one of expectation and access to your readers. Readers going to a website, expect it is up to date with current information, and that it might have changed since their last visit. Readers of an ebook, realise it may be out of date, but deal with it, and are not expecting it has been updated - and you very likely have no way to tell them.