Spacing and size is important, one nice thing about traditional scene based images is that they tend to be either square or portrait which gives one extra room at the top for text.
Of course for full cover scenes this can be some awkward, non-critical drawing (e.g. sky).
That was one nice thing about covers that used inset images.
BTW notice that really sexy looking grayish blue fellow on the left in the first picture! Woo hoo! Love me some limbs! =p~
I think they idea is that so much tends to happen in any given book that the title has to highlight certain parts of the book, and wanting the cover to reflect that title is what the author is waiting on. Of course, to be fair, in advance of writing the book, the title is based on what readers “think” the next book is going to be about (e.g. why he wants beta demons to vote/suggest title)
I.e by the end of book 2, it looks like book 3 is going “there” so title should reflect there, whether the book gets “there” or maybe goes further, is a different question.