It's quite enlightening in explaining how a work may have close points of similarity without that constituting proof of copyright infringement. The details are complicated, but a key concept is that of Scenes a faire ...
- those elements of a work "that necessarily result from the choice of a setting or situation,"
For instance, if I set a story involving a man stranded on a desert island, scenes a faire might include his trying to catch fish, trying to break open a coconut, growing a long beard, trying to signal a passing ship, and building a raft. As they're highly likely developments from the scenario, I wouldn't be infringing the copyright of, say, Castaway. I suspected this would be how it worked, and I'm sure much the same applies if the core scenario is a person living the same day over and over: it's fairly predictable that any competent writer would have the protagonist trying to capitalise on the situation of having no consequences beyond the day (e.g. commit a crime, try to seduce someone, etc).
Given the existence of scenes a faire, the issue of plagiarism-or-not hinges on the differences between two works rather than the similarities, and the differences were what swung the decision in the Arden v. Columbia case.