What they're talking about here is the "do it well." They're making an argument that doing it well involves repackaging that one thing you're doing for multiple audiences.

Content is half the battle. Distribution is the other.

Don't forget the third half; getting people to give a damn (i.e. marketing).

A comment I read somewhere about Rocketboom often comes back to me. It was something like this:

"They made a halfway decent video show....and then got it played everywhere. The everywhere was the real value."

The blog post linked about is not about making a video show, it's about the everywhere part of the equation.

I'm saying that the one thing 37signals does is making and selling productivity web apps. They've managed to find a great synergy between selling their "real" product and their marketing - which includes their blog, conferences, the "37signals way" - and they are talking about selling the byproducts of their marketing.

My point is that this isn't necessarily always a great strategy. If you're making plastic widgets, I'm not convinced you should spend effort on selling "working with plastic" e-books.