Display Suite was born out of the Node Displays module. The first version of this module took over the display fields screen of CCK because we wanted weights and labels per build mode and an easy and simple way to give our clients the power to alter the look and feel of their nodes. It quickly became a powerful module which was able to add extra fields, build modes and had integration with views.
Developers tend to think further, so after a while we completely broke the dependency with CCK and created the Node Displays Contributions project which at this time of writing has support for CCK, fivestar, ubercart and search. Search was our most coolest implementation at that point, since we're able to completely override the results page and also had tight integration with Apache Solr.
The ultimate step to the Display Suite came when we brainstormed to add build modes to user profiles. That's when we refactored the code of ND so all objects can be passed to the API. Modules implementing the API get fields, build modes, plugins, views etc for free and only need to create 2 or 3 functions to benefit of this power.