Together with Daisy and Apache Lenya, this makes (at least) three important OpenSource CMSes based on Cocoon! User expectations vary a lot when you talk CMS, so in my opinion it's good to have diversity - also because these guys know each other well enough to take advantage of the friendly competition to improve their products.
And don't forget the Apache Forrest publishing system, which is also built on Cocoon and works wonders in publishing and organizing content from very diverse sources.
Activity in the Cocoon project itself has slowed down in the last year, and these news show that it's more a sign of maturity than anything else. Cocoon 2.1.x is "done" in many ways, future versions will bring big improvements, especially in terms of ease of development, but the power and stability of these CMSes is a testimony to the quality and maturity of the 2.1.x code.