The standard of flying is the same, but the skills required are not.
An ATPL requires the ability to manage yourself, your crew and the aircraft in a complex technical environment. Phrased like that, the differences with an IR are obvious.
Perhaps we in Australia are only just now realising that the step from CPL/IR to ATPL should ideally have very little to do with stick & rudder skills. Ideally being the key word - I'm not sure the new requirements change much in practice, but they are perhaps an excessively bureaucratic step in the right direction.