If you value your position in the market it may be a mistake to control too much. Amazon’s eBook system the Kindle does not allow the user to purchase eBooks from suppliers other than Amazon. The Kindle rather tightly controls the environment in which eBooks can play. Sony has a rival eBook reader, which seems to be very similar but may have been losing ground to the Kindle. Perhaps the realisation that they cannot beat the Kindle at the game of selling a closed eBook reader has led Sony to a software upgrade that allows the user of a Sony ebook PRS-505 to upload any eBook in the PDF format. eBooks.com announces that it has 130,000 titles which are now available for the Sony reader. This relative open-ness may give Sony an important advantage.
I think Amazon will resist the pressure to make the Kindle a really good system for surfing the web, but the pressures to do that must be increasing. Once that happens any pure web digital edition will be usable on the Kindle. At that point they get outflanked by web editions as well as (probably) PDFs. Proprietary formats are fool’s gold. For the proprietor as well as the customer. You will find out a lot more about these format wars and the limitations of proprietary formats and DRM at the TeleRead blog.