That weekly exp event increase the base aion exp, and then all other source of exp is multipling based on base exp.
Lets say without any event we have the base exp at 1 ( or 100% )
a mob that gives 10exp without any amulet will give
20exp with 100% amulet
30exp with 200%amulet
So the amulets , cake buff, berdins and stuff multiplies the exp based on the base exp, but does not increase the base exp itself.
Now we have the weekly exp event which increase the BASE EXP by +100%. So the base was 1 and now increased by +1(100%) total of 2 ( or 200%).
So we have a new BASE E