In the section:
Stepper drivers vs Stepper Controllers
It is claimed: "a very small stepper may be driven directly from the controller", wouldn't that apply solely to unidirectional stepper motors?, since a bi-directional requires a phase change.
... with a "H-bridge"-setup and 4 transistors per coil (or 8 for a bipolar motor) you can switch the coils accordingly between Vdd and GND in either direction.
But unipolar requires only one transistor per coil, so is much easier to build and control ...