@ Check Airman: Yes there is some demand : APU bleed by itself pressurises the water systems and the hydraulic reservoirs, and of course the bleed pipe from the APU forwards, and seats the seals, so it uses some airflow and pressure but not a huge amount.
Doing it this way, also gives the APU hot parts a little longer to stabilise, before hitting it with the very big load of the pack(s).