I can't help but think this is the establishment Pubs (DC is right across the street) making sure the candidates that are most likely to tear down the govt hegemony are handicapped in getting the nomination. I think they don't consider Paul a threat and Romney is a go along get along blue blood technocrat so he's "their guy". Gingrich although he's from the DC culture has been clear he would make big changes and Perry has been specific about changing DC as well.
Actually the district requirement, seems to be a firewall against NOVA, which seems to be why it’s there. By requiring a candidate to have support in all the districts they ensure that just canvassing NOVA and the area isn’t enough.