It's more of an effort to become more of a unified region* (and allow HR to reap some of the benefits from the capital), but you're right in that both are well established. The argument is that the two markets are distant yet close enough to try it.
Norfolk is just under 90 minutes from Richmond, and roughly the same number of miles. The furthest northern point of the HR DMA is Williamsburg/James City County, which is about halfway between both DMAs. But I agree on the distance...that stretch between Williamsburg and Richmond is a bit of a snooze. :-P
Same for the amenities, both markets have their own separate set of media outlets, not to mention airports. One of these days, I'll tell the story of how the Cavemen sitcom pilot inadvertently implied how Norfolk and Richmond are closer than it seems.
/As if NCIS hasn't been doing so for years!
*//A problem that's plagued HR for decades