It doesn't matter, actually. Some publications will have style sheets that dictate the usage, but both mean exactly the same thing. The verb follows the form of "to lead." Some argue this, but common usage dictates that both forms are correct.

sigh

It's like lit and lighted. Just a matter of preference.

When I started noticing it I looked it up and found it was correct.

Apparently the standard is pleaded and they say pled is colloquial. I am certain have read pled in older books

discussion here: http://www.quickanddirtytips.com/education/grammar/pled-or-pleaded

When it's a human, it's "hanged", not "hung".