that is correct. the 4p is just the 4 that is easier to drive w/POS consumer headphone jacks.
I've read that it sacrifices a little bit of quality over the straight up er4, but you wouldn't notice.
I've used the 4, the 4p, the 6, the sure e2...
any BY FAR....the most "user freiendly', feature packed, AWESOME sounding, ass kicking isolation was w/the cheapest model M-Audio. I think its the E-10. $99.
smokes the er6. rivals the 4 easily. has excellent isolation...super comfy...and the fisrt 6 inches of wire coming out of the ear piece is able to be molded around your ear so that they stay on even if not in your ear.