The reason for the new wave of gearboxes, a la iShift, AS-Tronic (called "automated manuals" I believe) etc is two fold.  Firstly there is the fuel economy problem where full auto's give poor fuel economy.  Secondly even the newest full auto boxes are constant-mesh type boxes and are unable to deal with the torque output of the larger new generation engines.  That is why you can only get it up to 340hp with Scania and why Volvo have none as they did away with the 340hp B!2 a while ago and the B9 starts at 380hp.  Interestingly Volvo always said you couldn't have a full auto over 360hp while Scania always said you couldn't over 380hp (The K114/124 in an SP is a 360/380hp engine), yet they both use the exact same gearbox!!!

I do know that there is a restricted option for I-Shift and AS-Tronic.  Ulsterbus Ayats Coaches have the restricted AS-Tronic and I beleive some of Callinan's I-Shift coaches have been restricted.  In this case they only have auto mode with the driver basically only able to select D. N or R.  I don't know why alot more of the fleets haven't latched onto this option.