I think there is no point in comparing DEX with DipTrace. They obviously belong to different market segments.
DEX is on par with toys like ExpressPCB, KiCad, gEDA, DesignSpark, Freepcb and the like. They can be used to teach people the basics of pcb design, but nothing else. All of those of course have 3D preview and autorouter, which are basically useless for that kind of software. 3D mode's primary purpose is to verify collisions with mechanical parts in 3D cad (Catia, Solidworks etc.). this implies that the pcb cad has to be able to export ITEP and/or IGES format to be useful, otherwise it's only "+3 to wank factor". I know quite many pcb designers, and none of them uses autorouters/autoplacers. And we're talking Mentor/Cadence/Zuken level autorouters here.
Diptrace and Eagle i believe are meant for smaller businesses and hobby use, in other words people who cannot afford or don't need hyper expensive packages. DipTrace of course also has 3D mode (but pretty much useless thanks to lack of STEP/IGES import and export) and autorouter (which surprisingly can produce half-decent layout, which is an achievement for an autorouter). I also think that DipTrace developers are pretty responsive to feature requests, unlike Eagle or bigger players.