My biggest issue with both of those studies, is that they involve self reports with respect to bystander involvement in an emergency. I can think of few other issues in social psychology in which self reporting is going to be wildly out of touch with reality. The only other area in which I can see self reporting being even further out of turn with reality is the subject of conformity. The biggest factor influencing bystander involvement in an emergency is actual experience or training in handling such emergencies and how to resolve them. If you want bystanders to identify a real rape and have them intervene, then you need to train them to identify the difference between consensual sex and non-consensual sex and then train them on the best course of action to stopping the act in question and reporting it. There are numerous examples of studies in social psychology where people self report that they would do X and when put in that exact situation in an experimental setting actually end up doing Y. Situations where the subject is a bystander are among the most notorious for their disconnect between reality and self-reports.

Any study that measures the real impact of porn is going to involve measuring real incidents of rape witnessed or committed by a statistically significant population or porn viewers. Barring actual incident levels, this is crappy research. Asking questions like "Have you ever witnessed a rape in progress? And if so, did you do anything to report it or stop it?" and comparing those numbers to porn viewing habits would be far more valuable. At least in that case it ceases to be based on self-reports of behavior in hypothetical situations and is instead based on correlation of historical fact with porn habits.

Lastly, and I know this is an ad hominem attack, but judging by John Foubert's other research interests, I'd consider his rape research to be tainted and likely to be skewed in favor of demonstrating correlation where there isn't one or demonstrating correlation which is of no consequence but is sensational. Judging by several of his other published papers, Christianity and Spirituality primary areas of research for him. This puts him among a group of people who are impartial and very likely have an agenda with respect to the issue of pornography. ref: http://okstate.academia.edu/JohnFoubert

Do you have any research that compares actual incidents of rape and porn?