When the very first iPad was released back in 2010, Apple also introduced the concept of iBook and thus stepped on the ebook market to try its luck in the still growing world of e-reading. A lot of people speculate that Apple is going to dominate the competition, and that eventually e-readers like the Amazon Kindle might become obsolete. It turns out that it is not that simple.
With the introduction of the Retina Display a whole new different universe is created, a universe of sharp colors and bright lights. It is indeed wonderful for watching videos and playing games, but in the end it does not compare to the experience offered by the E-ink technology for simply reading text.
The iPad has been designed to perform multiple tasks and is really a multi-purpose gadget. Thus it would be pretty futile to ask that such a device be the perfect option for the act of reading. Even if text rendering on the iPad screen can be viewed extremely well, thereís no denying the fact that it actually looks like text on a computer screen. On the other hand, E-Ink really gives you the impression of reading an actual book and your eyes donít become exhausted at the same pace while reading from an ebook.
On the other hand, the act of reading digital magazines is much better performed on the iPad. The colors of the images certainly look better on the tablet screen, plus the screen can accommodate the whole page without you having to scroll up and down.
Source: Is The New iPad Retina Display Really Better Than E-Ink For Reading? -- AppAdvice