Problem with CHAdeMO: not enough power (500VDC and 125A means 62.5kW peak). It's completely fine for smaller packs like in the Leaf, not enough for a pack 3.5x as large (the 85kWh Model S). The superchargers can handle twice the power (120kW). Problem with J1772-DC: Not ready yet. Given the choice between the two, I think Tesla would have chosen J1772-DC (Tesla's connector is very similar), but unfortunately it's wasn't ready when Tesla had to finalize their car. As for access to the Supercharger network, that's largely orthogonal to the connector. If Tesla went with a standard connector, I don't think they would have built this network (but rather would have pushed for more publicly funded chargers, like other manufacturers have done). Their goal for this network is NOT to provide charging for EVs overall, but rather to provide an exclusive perk to Tesla owners. At this point, running a fast charging network is doesn't make economic sense (even with charging fees; the current networks only exist because of government funding), so even if Tesla can build a network that other EVs can use, they won't. This is esp. true when you have cars charging at half the speed the charger can handle.