Umm......I think that article is referring to something very different to what we know as Pitch Pine as reclaimed from Mills and Warehouses in this country.
I've seen many beams of at least 7" x 5" section in 12' lengths in very straight grain, without a knot in sight over the entire length.
As for why it is called PP....maybe because every so often you come across pockets of pitch? Also there seem to be at least 2 distinct varieties available ex mills - one is the tight grained orange/brown stuff I mentioned, the other is an equally heavy but much harder, wider grained wood - the smell is the same, but it gums up everything with resin and also has huge live knots.
Chris.