I believe what Lesley King is saying is that a standard power of appointment cannot be used to transfer assets out of the original trust to an entirely different trust. An express power to transfer assets to another trust is usually needed for that to happen. By contrast, an appointment onto bare trusts is simply a modification of the terms of the existing trust, and would be possible under the power quoted.
I’m not sure, but is the point here that the power is not itself used to transfer assets out of the trust. It is very common as you say to appoint a ‘bare’ trust of assets but the transfer of assets is still a separate supplemental exercise.