If DC adapters are so prevalent, why is AC used in construction by default?
Transmission/Functional reasons:


AC is cheaper -- There is less power loss from generator to end user.
High voltage is cheaper to transport --  Power loss is I^2 * R.  R is a constant over any line. For the same amount of power (watts) P = IV.  So we can decrease the power loss by increasing the voltage. - This leads us to transform-ability.  I can easily run AC through a transformer to jump the voltage up or down (with a corresponding change in current).  Doing so with DC requires several more steps.
[addendum] If we were just lighting and heating with electricity, we wouldn't care AC/DC from a functional point of view.  However, lots of things in our houses use motors, and AC motors are cheaper and last a lot longer than DC motors. However, when we were first wiring neighbourhoods, this wasn't a factor.