a_g123:
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.
Read the Allegro A4988 datasheet to get an idea of how much thought and complex engineering has been built into the a4988 driver.
...R