It is a bit fun to be honest, how HTML5, that Apple use to crusade against Flash, is also coming back and biting them in the behinds when other companies refuse Apples rules.
Okay, let's summarize the old discussion again.
Apple pretended to champion HTML 5 for very simple reasons: Flash is a cross platform tool that allows the creation of STANDALONE applications - the app that you build for the iPhone would also run on an Android device or a Mac or a PC. Cross-platform capabilities are very dangerous to you when you want to lock-in people to your platform. Also, the Flash video format runs on any supported platform and since Apple wants to establish its own DRMed video format as a de facto standard, of course they don't want a third party technology competing with their own technology stack on their own platform.
HTML 5 on the other hand still is not an official standard and it requires a web browser to run. No standalone cross-platform apps, not even an official standard for video yet. So it's not remotely dangerous to Apple, especially since it's still more comfortable to use native apps (sold through the Apple App Store) over web apps. And Apple even looks good in the eyes of many users because they boast to support "an open standard" instead of "the proprietary Flash technology". Everybody who works in IT knows that this is all just BS, but the average Apple customer does not have enough technical background knowledge for making a proper judgment.
I'm sure that at this point Apple hates web browsers as much as Microsoft hated Netscape back in the day and that Apple would love to remove Safari from iOS so that their users would be forced to use apps for everything. When you sell platforms, open technology and open standards that make customers independent from your products are your natural enemy.
Companies like Amazon and Google have one major advantage in this game: They don't need to sell platforms or hardware in order to be successful. They ARE their own platforms and they are completely independent from hardware. They don't care what hardware you use because their software and stores work equally well across all platforms.
Apple's success is dependent on both their hardware AND their software; iTunes is only successful because of the iOS devices, and the iOS devices only sell because of the content and software fueled to them through the iTunes stores.
Now having a browser-based reader application is amazingly cool for Amazon customers. I'm running it here on my Windows notebook at work (in Google Chrome) and this thing works exactly as I expected it to work. It knows the position where I stopped reading on my Galaxy S2 or my Kindle at home and I don't even have to install anything on my machine to continue reading. I can now roam around the server room and read on any damn machine there if I want to while I wait for some computer jobs to finish. I love it.
Apple, on the other hand, has not even managed to ship an iBooks version of Mac OS X, let alone one for Microsoft Windows or - heaven forbid! - Android. No wonder that iBooks is not even remotely as successful as Kindle. Amazon, because they are not dependent on hardware sales, can provide a solution that is 100% customer oriented. Apple -has- to make compromises in order to protect their hardware sales. And in this case, these compromises make iBooks a less flexible and thus inferior offering.
It's just a question of time now until other content providers follow Amazon's example - or even use their platform - and publish their digital content using pure web technologies. As a side-effect, this will level the playing field between Android and iOS even more, since a huge amount of those apps in Apple's App Store are actually just eBooks, videos or music encapsulated in a reader/playback application.
Anyway. This is web reader is a win for customers and for Amazon, and it's big loss for Apple.
The irony is that the web, which made a lot of Apple's late success possible, is now turning against them. I guess the web simply doesn't like closed, proprietary technologies and attempted vendor lock-ins.