Well, Apple owners aren't too bothered by this because the Apple platform remains the most open and versatile in terms of content, including reading content. There are still apps for every major bookstore on the IOS platform, along with independent ebook reader apps like Bluefire and Txtr. All that has happened is it has been more inconvenient for Apple customers to buy ebooks. If we look at access to magazines, there is FAR more content available on iOS than any other platform, and there is likely to be even more when Apple rolls out it's Newsstand feature with iOS 5 in a couple months.
As for iBooks , Apple certainly has the money and engineers to make iBooks a worthy competitor to Amazon and B&N. I'm hoping that they will eventually do so, maybe as early as with the iOS 5 upgrade ( that famous one thing more). Realistically, though, they are right now more focused on rolling out features like Newsstand and iCloud, so iBooks will continue to be second tier for a while longer, IMO.
This isn't a problem for me or more techie consumers, but will be a problem for those iOS consumers who really only interact with their devices through apps. They will tend to go to iBooks , which means fewer sales for other booksellers and worse choices for those consumers.