Yes, he can get in there... but reg can still leave pretty easily. And warpstone and cloak of the night have their own serious disadvantages (isn't cloak of the night general only?)
Not only that, but triple stacking slows only takes a small amount of cash, but a warpstone costs a lot.
Yeah, they are pretty bad expensive solutions, but could be used. I think with Erebus though, he gets in with swarm, hits bite and then Reg is in a lot of trouble, especially if Erebus has charm. Personally, I am usually using a minion build with Erebus so lack charm, but I don't have any problems keeping up with Reg once bitten.
The great thing is that if you are in a 2v2 or 3v3 situation, you have taken Reg out of the game at least. You have then sandwiched your other opponents and can hit on their weakest.
The biggest problem I see with Reg, is that people don't watch what he is doing. He is very fragile but easily counterable just through knowledge. You know you cannot go down to under 500HP, you will be sniped, so you have to play to that. You watch where he lays mines or get a Totem, that skill is also wasted.
Watching a Reg where he has nothing to do, because people are avoiding his mines or his snipes are just being wasted is a very sad sight.
If you are letting him sit on his own in a corner of a map, taking down creeps and towers, then you are in for a world of pain.