Pacific Northwest Ballet circulated excerpts from a wonderful essay by Anita Finkle (that they had commissioned in the 1980s for their first performance of the work) -- the gist of her argument is that all the couples in the work, both human and fairy, were incomplete in some fashion, and that it's only when we get to the second act that we see an example of mature, adult love. It's not an exact example of Petipa's well-made-play structure, but I thought it was a compelling justification.