I do not have access to the case presented by Lady F., but the precedent she cites is here:
http://docs.justia.com/cases/federal/appellate-courts/ca7/11-1708/11-1708-2012-08-20.pdf The gist of the argument in that case seems to be that having the opportunity to copy something can be used as very strong evidence that the work was not independently created. Independent creation is an absolute defense. If I can prove that I wrote a novel by myself with no possibility of having seen another word for word identical novel, I cannot be found to have violated its copyright. Access can also be used as evidence to prove that copying has occurred if the works are sufficiently similar. But to accept that infringement has occurred it is not only necessary to show that it might have been copied, but that the portion of the work that was copied is sufficiently unique and important in its expression to be protected by the copyright. I cannot find anything in that opinion that relies on a test of whether an "ordinary observer" could or could not tell that the song lyrics were illegally copied. I think the reasoning by the court in this case leaves the possibility that the West song may have been influenced or inspired by hearing the plaintiff's song, but that the similarity of the material does not constitute infringement.
The problem is that if the courts enforce copyright against an accused infringer just because he could have heard a similar song to the one he wrote, the world will be a lot worse for the regular humans who try to write original songs. Given the enormous numbers of songs in the world with valid copyright to which most of us may have access, it is far more likely that a songwriter will find he is being sued by a professional rights organization or publisher than the other way around. If access to the similar song plus a vague or partial similarity of tone, use of common phrases, story line, types of characters etc. proved infringement, a lawyer could probably haul hundreds of thousands of songs into court.
As for summary judgement, there is nothing new or unique to big corporations or small plaintiffs using that to avoid an expensive trial in which the facts are not in significant dispute, and the decision just requires legal interpretation. It is a decision that is subject to appeal.
I do not know anything about why Gagga is suing Rebecca. The options to sue someone for the injury you receive from responding to their lawsuit are limited.
http://en.wikipedia.org/wiki/Malicious_prosecution It seems to be a heavy handed response unless the original suit was clearly an attempted shake down or unless Gagga et. al. are trying to discourage other people from using their legal rights to pursue what they believe is a justified infringement action against her or her publisher. It is probably a very bad move from a public relations standpoint, and lends itself to cries of legal thuggery.