Charles, you might want to read some of Peter Singer's writings on this point.

Robin, it's clear that relative frequencies exist and matter somehow, even though it might seem like they shouldn't (e.g. because of the ordering problem described in Dr. Bostrom's paper). We observe random events with nonuniform distributions to occur according to the distribution, as opposed to uniformly. We don't live in an extremely bizarre, acausal world even though there are an infinite number throughout spacetime, because the laws of physics are such as to make bizarre worlds rarer than normal ones (even though there are many more possible bizarre worlds than normal ones). "Difficult topic" is probably an understatement.