From his post, it appears that ML handles exceptions by allowing code to add new constructors to the 'exc' type at run-time. This is effectively indistinguishable from the GHC implementation of dynamic typing, which uses typeclasses.
Without some sort of dynamic type casting as used in ML or Haskell, then it's not possible to implement an exception handler that can extract information (such as type) about an exception. All you'd be able to determine is "some exception was thrown".
Yes, ML is adding new constructors to exn type at runtime, but this is different from GHC implementation of dynamic typing which uses typeclasses, because GHC does not add typeclasses at runtime. Take a look at ezyang(who is a GHC developer)'s comments in the post.
I repeat that this is extremely obscure and probably only interesting to people like ezyang. He is engaged in the discussion, so I guess the post was not pointless.
Without some sort of dynamic type casting as used in ML or Haskell, then it's not possible to implement an exception handler that can extract information (such as type) about an exception. All you'd be able to determine is "some exception was thrown".