My first thought was "chimp ****, really?"
Having got past that, I can sort of understand the findings. I think if you redid that experiment and added in a measure of brain activity you would find a difference in what's going on in men and women's brains. My layperson's hypothesis is that women perform more processing on the images that they are exposed to, whereas for men it goes straight from eyes to nether region (generally speaking, I'm sure their are some people who react in an atypical way for their gender). On the other hand, maybe women process less in terms of physical arousal, men have a reaction based on "would I want to be having sex in this situation?", whereas women react on a "is this a sexual situation?" without (their body) adding in a judgement on whether they would want to be involved.
As for the differences between physical readings and self-report it could be that a) women were reporting in terms of what they would want to be involved in (rather than if they were physically aroused) and/or b) they recognised the physical arousal (so it's not a case of women not knowing what they are feeling), but didn't want to own up to finding it arousing (there's quite a few things that arouse me that I wouldn't necessarily want to tell someone else "yeah, that totally turned me on").
I think this is quite an interesting topic, I'm a bit of a prude, so would probably never get around to reading up on studies in the are, but I'm curious about if this has any possible link to men and women vs ****. Most anecdotal evidence suggests that men love them some visual stimuli when it comes to ************* women I don't see talking about it as much (but maybe I just don't look in the right places :P). Maybe men react more predictably to sexual imagery because their arousal is more stimuli based, whereas women tend to self arouse through thinking about things (rather than looking at them) and so don't process in the same way as men do.