What the difference between the Honda Element EX and the EX-P ?

Just different trim levels.  

agreed.

It's my understanding that EX used to mean the trim which had black panels on the outside along with the car color, and that EX-P meant that the black panels were painted, too -- so the car was all one color.  Around the 2007 model year, this changed and they stopped saying EX-P and went back to using EX for all the models at this trim level.  As far as I know, the P just meant "painted," which used to cost $500 extra.