In git, a cherry pick essentially just looks at the diff specified by that revision, then applies that diff as a new commit. The system doesn't record the context (unlike with a merge where you at least know the parents).
darcs system is way too complicated to get into in a short comment reply, but the basic idea is that if you cherry-pick a commit you get all the context along with it. That's because darcs stores a series of patches rather than a series of tree states.
One nice thing about git's way is that since it's just pulling a diff, you can cherry-pick from anything, (e.g. add a remote that's a totally separate unrelated project) as long as the diff applies cleanly.
from 10000 feet, cherry picking in git is "get me this single commit from that branch", in darcs it's "get me this commit and every other needed to get it to apply correctly in this one".
