The addons for 1.8 are included in asterisk, look at the menu in “make menuselect” while compiling asterisk.

The reason for including it is because when we occasionally need to change the internal API, it’s difficult to remember which version of the addons package goes with each version of Asterisk. Additionally, changes to the addons packages rarely got released on time in the past. It makes it a lot easier just to include them directly in the main distribution, default disabled.