Why? Well, Kindle Tweeting under 2.5 sounds like it is more than a bit cumbersome. And the same sort of hardware limits will be present for the Nook, Sony Readers, etc.
From Lance Ulanoff, PCMag.com:
I love reading books and my New Yorker on the Amazon Kindle. But let's be clear: the e-reader is a long way from a computer or even a smartphone. As Amazon adds more features, the limitations of the device become increasingly clear.
Navigating beyond simple page turns often involves a combination of button presses and toggles. Even then you may have to hunt for things under the sometimes inscrutable interface. Finding the social sharing features, for example, wasn't immediate obvious. (They're under the settings.) Set-up requires you go through the Kindle's still experimental and very limited web browser, with the Whispernet connection on.
Once there, I used the Kindle joystick to navigate to and select the Twitter account box. I signed into Twitter and connected the account to my Kindle account. Twitter verified my login and I was able to leave the hoary browser and return to my regular Kindle reading interface.
A bare minimum of guidance
Once again, there was nothing on my Kindle page to indicate anything has changed. I had to move my cursor around on the e-ink screen for a message to appear at the base of my text telling me what to do if I wanted to create a note. Kindle's skeletal instructions in the settings told me I could share notes and highlights. I had to move my cursor around on the e-ink page to see a message that told me I had entered the beginning of the social sharing process. It said I could simply start typing on the Kindle's keyboard – something I've almost never done – or click the joystick to start highlighting text.
I decided to highlight text. As soon as I did, another message appeared at the base of my text, telling me I needed to hold the "Alt" and "Return" keys to "tweet/share". The next screen offered me a typing window and a character count (like any good Twitter app should). I only had 100 characters of my 140 allotment left because, as the screen informed me, the Tweet would carry a link to my highlighted text. Though QWERTY, the Kindle's keyboard isn't built for extensive typing. It took me far longer than it should have to compose a simple tweet. Still, I got through it and I assume I may get better at Kindle typing over time.
Once I finished and selected "Share" there was no indication that I had successfully tweeted out my message. On the e-ink screen, however, my highlighted text kept a thin underline and had a small, numbered footnote. When I highlighted it, my tweet appeared at the base of the page.
On my PC I found my tweet in Twitter, complete with a link to the excerpted text on a special Amazon.com Kindle Beta page. This was pretty impressive, and I soon realized that I could share passages of any length from any book or magazine I was reading. The Amazon page automatically features the book name and cover image, so there's no need to worry if you haven't shared the actual book title.
While I tweeted my passage to all my followers, I would also love to see the ability to tweet to, say, an individual over a Twitter direct message or to send the passage via email. While there's also a Facebook sharing option, there isn't any way yet to share text via e-mail.