1) The Adventure shock is the same body, spring, etc. but without the dampening adjustment or the lifetime warranty, free service, etc. It's a great choice for those on a budget. I have a Moab on one bike and an Adventure on the other and you cannot tell the difference.
2) The DDC's are a device intended to give you cartridge level fork performance from the antiquated damper rod forks. The dampening on the existing forks is controlled by the flow of oil through a set of fixed orifices. The only adjustment is by drilling (changing the size of the orifice... but making it larger decreases dampening - bad) or by changing the weight of the fork oil....which works but makes the forks harsh over smaller bumps. This is all about the dampening; spring rate is affected by the springs, preload spacers and sometimes air pressure....
The DDC's use 5 weight oil which is light enough that it has negligible resistance through the stock orifices so they are effectively bypassed. On compression the oil is now forced to displace the deflective disks in the DDC which offers a much more compliant ride than the damper rod orifices. a spring valve controls the rebound dampening rate much like Racetech's Cartridge Emulator/Gold Valves do for both compression and rebound. The advantages of the DDC is that because they bypass the orifices there is no need to disassemble the fork and drill out the damper rods like the RT valves.
Some people attempt to bandaid the forks using heavier oil, stiffer springs, progressively wound springs and sometimes by adding air pressure. These solutions can help with bottoming and fork dive but at the expense of plushness. The DDC equipped forks aren't harsh on the small stuff like rocks, washboard, roots, etc. but they offer vastly improved resistance to bottoming and keep the tire in contact with the ground for improved control.
I'm not a suspension expert and I strongly recommend a quick call to Rick or Todd at Cogent; they are happy to discuss the issue in more detail and point out solutions without any "upselling". I hope this helped.