Without reading through all the posts here...

My theory is that reading the past tense "plead" off a teleprompter while presenting the news is likely to cause the talking heads to misread it and say the present tense "plead" instead. "Pleaded" (it hurts me to even type that) is obviously much less likely to be misread.

Maybe the spelling should be changed to "pleed" (like "bleed") and "pled" (like "bled"). Bleed/bled don't seem to give people any trouble. Or even "plead" and "pled", maybe?