If they are the same page, is one of them
www.domain.com and the other domain.com? That is possible depending on the structure of the inbound links and internal linking.
Or
If they are two seperate pages, they just happen to have what it takes. I read somewhere long time ago that you won't get a 3rd page listed in that serp due to spam control. Not sure how accurate that article was but it seems to hold true.