This slideshow made me laugh.
I've been a Twitter user now for two years, and I'm intrigued by its success.
You can attribute its success to its incredible simplicity, leaving the wider community to develop applications and 'clients' that anyone can chose to adopt or ignore.
You could attribute it to the character limit, meaning that no-one has to worry that they have to put much work into Tweeting (something that holds blogging back to this day), yet also short enough that clever-clogs can innovate and play games with the limitation.
You could attribute it to the ingenious (and incredibly obvious... with the advantage of hindsight) tweak to instant messaging. Take something that is already incredibly popular, but make it more public, more 'many-to-many'.
You could attribute it to its avoidance of rules. Things like the @ way of addressing other Tweople and hashtags emerged from the community. Community sourced innovation lives or dies according to the community's regard for that innovation, so QED only good stuff comes out of it at no cost to Twitter.
However you cut it, perhaps the most important contributing factor to Twitter's success is the heartfelt derision from non-Tweople who don't get it that simply serves to harden the loyalty of those that do, and loving derision and teasing from the Twitter users themselves. Even the fail whale worked to Twitter's net advantage.
Here's a fun take on Tweeting for a Friday. In the meantime, if anyone is considering a Web innovation, the list of success attributes above might not be a bad starting point in shaping your own innovation and improving its chances of success.
