Any system using interrupts will use quite a lot of the CPU resources. In a RTOS you may have to run the scheduler after each interrupt to see, if any high priority task became runnable due to the interrupt.
Thus, the job done by interrupts and scheduler is similar to that of the EEPROM checker, even if the high priority tasks do nothing for a long time.
I agree that the null task could be as trivial as a single WaitForInterrupt instruction or a single branch to itself instruction, which will exercise only a small part of the CPU, but this is not the point.
Paul