Why is Twitter getting huge?

So, I signed up for Twitter a few weeks ago and was utterly amazed at how much its used. Most of the big shot tech luminaries are on it, (Guy Kawasaki, Kevin Rose, Chris Pirillo, Leo Laporte, etc.) and they are also VERY frequent posters. (Robert Scoble's there at least 5 times a day) Also, the number of followers each one has is incredible. Twitterholic has these stats and right now, Leo has over 37,000!! What's interesting is that he only has 900 or so messages posts (or "tweets"). Scoble is in 5th place in terms of followers but has over 12,ooo tweets. It's interesting the type of people who are followed. Seth Godin never posts anything unique - its simply the title of his daily blog post, which I already get in my RSS feed. Yet, over 5,500 people follow him.

The TWIT crew are even giving out their twitter names as of late - of course these are predominately those I mentioned above, but they are almost skipping out on their blog URLs. John C Dvorak used to mention his blog a few times a show (it was a running joke), but now Leo only mentions it at the onset and then they all repeat their Twitter names throughout. Neat how it has changed.

To answer my original question - I think it'll only continue getting bigger as long as the big shots keep using it. I'll also be interested how they initiate some direct cash-building exercises.