Robin2:
This does not make any sense as an argument for using an L298. An Arduino has even more work to do when driving a stepper motor with an L298 because it must control the timing of signals on all 4 motor coil wires rather than on a single step pin.And if you are thinking of also burdening the Arduino with current measurement and current limiting ....
well, you have a point there, A4988 and the better DRV8825 takes care of much of the stepper motor driving.
however, the motivation is slightly different, i think there are some advantages of using the mcu / arduino for that matter as the motor driver. the idea is that L293D and L298 are high current devices that does the motor control, the idea is to separate the 'power driving' stages (i could have use a mosfet h-bridge for that matter) from the control stages. this is so that if a low cost L293D part burns out for some reason, it can be swapped with a new piece at a lower cost.
of course A4988 and DRV8825 aren't that expensive these days, and i think using those stepper drivers makes sense as well. A4988 and DRV8825 goes at a slight premium compared to L293D going for around $1 on ebay. while L293D is around 40c a piece on ebay.