Not entirely true, addons for minecraft are called mods
Mod as in Modification
Touche. However, most of the time, those are either total conversions, or major conversions of the game. However, in Blockland, there are not really any add-on's that I can think of to be major or total conversions, thus not really being able to be considered mods. However, they are minor, or at least not that significant, and are considered add-on's.