It's because the women are attracted to the BMW and Mercedes logos. They still probably don't know much about the technical merits of those cars and I doubt it's the muscular chubby stance of the M5 that is attracting them. It's the brand and that's all. They probably don't even know what an Acura is... thus no attention
I think you're right about the women being attracted to the prestigious logos. However I think there's more to it that just that.
While I personally prefer the exotic shape of the NSX over that of a modern high end sedan, the NSX looks sorta outdated sitting next to an M5. Modern cars have a decisively different appearance that would best be described as chubby and muscular, giving them a sense of presence (i.e. dominating and strong). Both the R8 and the new NSX have this modern look too. By contrast the original NSX looks lean and sophisticated. Since young women are one of the most likely groups to be in sync with current style trends the M5 will be seen as a young/hot car, while the NSX simply looks old.