In an answer given to How can I politely remind ATC that I'm waiting for instructions or clearance? by @Mark, he quoted part of AIM regs:
a. Pilots of departing aircraft should communicate with the control tower on the appropriate ground control/clearance delivery frequency prior to starting engines to receive engine start time, taxi and/or clearance information. Unless otherwise advised by the tower, remain on that frequency during taxiing and runup, then change to local control frequency when ready to request takeoff clearance.
NOTE- Pilots are encouraged to monitor the local tower frequency as soon as practical consistent with other ATC requirements.
REFERENCE- AIM, Automatic Terminal Information Service (ATIS), Paragraph 4-1-13.
b. The tower controller will consider that pilots of turbine-powered aircraft are ready for takeoff when they reach the runway or warm-up block unless advised otherwise.
I have bolded paragraph b because that is what I am asking about here. Why is the tower controller to consider turbine-powered aircraft to be "ready for takeoff when they reach the runway"?
Why are non-turbine engines (piston?) not ready? What does this paragraph cause the tower to not have to do?