From the article intro: "If evolution is the cornerstone of life, that's certainly no less true in the electronic world. If you can't adapt — or fail to adapt in time — you're destined to join the ranks of the Netscape Navigators, OS/2 operating systems, and WordPerfect office suites of the world, as a warning to future technology developers that nothing lasts forever, and never in its original form.
In this light, EPUB 3 is more than just bug fixes and tweaks from the last version; it represents a major change in what an ebook can be. It's a whole new beast, you might say.
The ebook market has been going through its own kind of hyper-evolution in the mere four years since EPUB2 was released, and a flurry of new devices and document formats have come and gone in that time.
E Ink technology was all the rage in 2007 when Adobe, Amazon, Sony, and others were entering the market, however, and EPUB2 arrived to meet the new needs of these portable reading devices, with improved presentation capabilities, better navigation, support for DAISY accessibility features, and some advances in global language support.
But EPUB2, like its predecessor and contemporaries, remained a static format, in that its core only allowed for the reading of basic text and image documents."
Read the full article: http://radar.oreilly.com/2011/11/epub3-multimedia-devices-accessibility.html