I never realized this happened elsewhere, too. My
small-town post office has been doing this for
years -- clears a package as signed-for and
delivered the day before it arrives at my home. 

I always assumed it was just because rural towns
operate differently. They know when and where to
find me for delivery because everyone in this town
knows everyone else. And they'd never hand my
package to the wrong person because they know me
on sight.

But I guess it's standard elsewhere too. Kind of
defeats the purpose of signatures, doesn't it?