[gargravarr]

The key feature of ABS is that it prevents the steering wheels from locking up, allowing the driver to steer around the obstacle. On loose surfaces, ABS can cause braking distances to increase; locked wheels can dig into gravel and slush, causing it to stack up and increase friction. ABS is also useless on sheet ice (but then, no braking system is genuinely at an advantage there).

These are edge cases though, and ABS does generally improve braking distances. At the very least, it gives you a much better chance of avoiding the obstacle in your path.