Personally I think it’s force simulation and geo/projection libraries are the thing that have made it stand out. It seems to be the de facto choice for any mapping or simulation visualisations. It’s DOM selection mechanics are neither here nor there in comparison.
Having done a lot of geo-spatial web projects, I would, hand down, use OpenLayers as my go to over D3. Not that there is anything wrong with D3 and it is a great library but man it's a pain to maintain and extend a D3 mapping solution.
I just ported a D3 solution to OpenLayers for a client and they where over the moon with the speed at which they could implement new features. Mobile touch was the killer for them and made them finally bite the bullet and port, getting a D3 mapping solution to behave correctly on both the desktop and mobile requires a lot of wiring.
