How is Twitter changing the media landscape and why is it that fast?

Events like the earthquake in china or the Hudson river plane crash have shown that Twitter is the place-to-be for real-time information.

1. Why does Twitter enable such a fast spread of information? Has it to do something with its topology (compared to other social media) or is it only because of its short-message-style?

2. How is Twitter changing the media landscape? Are there still news reporter who do not use Twitter? Why?

...need some input. Thanks a lot!