Yes. It is easy to insert ads to the embedded video(YouTube). It's not the case with embedded Images.It only helps to improve the Twitter experience. I don't remember clicking on the images(when they allowed it) to go the Instagram site. Nowadays, I sometimes click on the Instagaram links based on the info provided.
They didn't want fragmentation of the iPad apps. Having it 8" instead of 7" makes the regular iPad optimized apps look better. Reducing the size to 7" levels would have some usability issues.
The site should have the capability to detect login attempt for multiple attempts - Show captcha
Same account login attempt from multiple IPs - show captcha
With the above: a simple time wait for next attempt could solve the issue for most legit attempts right?