AC adapter size

Why do AC adapters have to be so big?  Can't they be designed more compact to say, 1/4 their size, or about the size of a regular outlet but with more height/depth rather than socket stealing width? 

AC is used in homes because of the huge amount of power loss that would occur if a low voltage DC was supplied.  Even compared to a 120VDC line, a 3VDC line would cause 1600 times the power loss.  AC is also a lot easier to use because you can raise the voltage for transmission and lower it again for home use without using complicated methods.  The current power system is as good as its going to get right now, providing any sort of low DC voltage for home use would be impossible.