I should clarify... Yes org-mode has todo features, including calendering, scheduling, etc, but listen some of the talks Carsten Dominik gives where he explains his rational: http://orgmode.org/talks.html It's core is as an flexible note-taking app with all those features as extensions to the core, just like the document links, and timestamp features.

In theory, org todos are born as notes which you later realize are actually todo items. Taken in this light, it makes sense as a text editor extension rather than an app in its own right.