Sorry for any Ramblings and simpistic views here, just thinking out loud..
If you consider the two parts of a regular airline ticket, in consists of two parts. 1 - The part the airline has no control over and must pay over, taxes to governments and airports lets call these 'forced charges', and 2 - The fare paid to the airline to cover their costs (airplane, maintance, crew, meals, fuel) and make a profit.
Now think to airlines before the age of the fuel surcharge. They calculated how much it cost to operate the flight, be it the cost of buying and maintance of plane, crewing, operations, providing customers with food and crucially to this argument, how much the fuel cost. The airline then made sure they charged enough to each customer to cover this. Then they added the taxes they were forced to pay.
Recently, fuel has gone up and airlines margins were squeezed so they needed to charge more. It was clearly somebodys brainwave that this cost falls into the first bracket of what I call 'forced charges', and not the original fare secion of the ticket. This results in two advantages to the airlines, A) Their fares do not increase on the initial part of the booking form making the customer still think they're getting good value (I accept in europe this is largely now included in the first price of the ticket you see) and (B) theyre able to fleece more on redemption tickets.
If the bus timetable said £4 and you got on the bus and they asked for an extra £1 as fuel surcharge there'd be an outcry (here anyway!!)
Basically, I think this is just a cost the airline has a control over, and every airline will be able to control to different efficiency, and management of this is a part of their expenditure on a flight and is not a fixed tax imposed on everybody.