Unless I am totally confused I have never paid $11 to book a silver service taxi. The flagfall is something like ~$4.20 and the booking fee, whether by phone or internet, is ~$1.80. The taxi fare from my place to SYD T1 and vice versa is ~$25 and that is all I have ever paid even when I have booked a silver service taxi.
In Sydney, Silver service:
Current Fares - Effective From 1 July 2008
Hiring Charges:
$3.10
Distance Rate:
Tariff 1:
$1.85 per kilometre Between 6 a.m. and 10 p.m. daily
Tariff 2:
Tariff 1 + 20% Between 10 p.m. and 6 a.m. daily
Radio Booking fee:
$2.00 surcharge in addition to the fare.
Waiting time:
$48.00 per hour (80c per minute - less than 26 KPH)
Toll and ferry Charges:
The hirer must pay all road, bridge, ferry, tunnel and airport tolls that apply to the journey.
For Brisbane:
Where a Silver Service vehicle is requested when placing the booking, a $11 fee applies on top of the standard taxi meter rate.
For Canberra:
A customer placing a booking with Silver Service will be charged an $11 booking fee, as well as the taxi meter rate. This $11 fee provides for the luxury vehicle and Silver Guarantee.
So it all depends on the state etc.