Rogue30 said:
I'd venture to say that it has to do with the timing of the thing. You "copy an effect," usually a triggered one, when you are Responding to that actual effect resolving. Essentially, you copy an effect in the same window as when that effect resolved. You "resolve an effect," usually a passive one, at a time other than when it is resolving itself. Essentially, you "resolve an effect" in a different window than the one in which that effect resolved.
So in a practical, mimicking the other card kind of way, not much difference. It seems to be more of a timing/ability type kind of distinction.
Note that "Ours for the Taking" is unique unto itself in that it is the only thing we have that copies an "ability," including (most) costs and play restrictions.