That's correct. The ABS basically takes away the brake pressure as soon as the wheels block. On most surfaces this will shorten your stopping distance versus a human blocking the tires. It is never the optimal stopping distance though.

In terms of split second reactions, it's pretty much optimal still to just jam the brakes if you have ABS. It's much better than braking too little, which is what most non-ABS drivers would have done.

When you block the wheels in loose snow or gravel, it piles up in front of the tire and provides a fair amount of friction. This is usually the fastest way to stop, and one of the reasons that gravel pits along corners in motor racing are so effective.

That said, the point of ABS is in the rare event that you have to brake full power, the system automatically help you do it at a near optimal (slightly skidding) without additional input, and you remain full steering ability.

If you don't have ABS you'd need to train that emergency stop ability on a daily basis to even come close.

> Wikipedia backs me up but adds that it also decreases stopping distance on dry and slippery surfaces,

Many cars, such as my POS Ford Focus, use a single-channel ABS system. These systems will oscillate all four brakes even if only one is locked. Combined with the rear-wheel drum brakes, the ABS considerably increased stopping distances on dry road.