Is writing a webchat client some black dark art?
There's nothing much you need to know to write a webchat client. Campfire isn't high volume, so it doesn't need to be too efficient either. Last time I checked campfire processes a few messages a second. Heck you could rewrite it in PHP/MySQL if you were that way inclined.
Campfire didn't succeed because it was a good product. It succeeded because they marketed it to their "following" who bought into it.
Many times people will see a product or company and think "how simple, I could have made that ... why did they succeed?" Everyone has assets they bring to the table that help them succeed. For some it means they can create and sell a less than stellar product because they have existing leverage in a market that give them an advantage an average "Joe" wouldn't.
Are we really back to the childish argument of "this is so easy to build, would just take a few minutes"?
The point is, if you bought campfire, all you'd really be buying is the existing customer base.