Good point and we should certainly have mentioned it. AdBlock is using the same underlying engine that Adblock Plus is developing (adblockpluscore), which means they have the same performance when it comes to matching requests (there could still be differences in the extension itself but that was not measured in the study).

Source: https://github.com/betafish-inc/adblock-releases#intro and https://en.wikipedia.org/wiki/AdBlock