More generally, I am curious why the algorithm used by Simplify prefers anything besides True, if anyone knows. Is there some reason for Simplify not to conform with its description in the tutorial?
FullSimplify[a^b (c^d)^b == a^b c^(d b),
b \[Element] Integers && d \[Element] Integers]
Gives True as well (all I did was replace Simplify with FullSimplify). Generally I just use FullSimplify. It can take a little longer, but many times gets a better result.