(max 4 pax incl pilot, 200 BHP, Single/Simple Engine)
Surprised no-one's picked up on this one, but those are the limitations of the
rating not the the licence. True, most people who do a PPL do it with an Single Engine Piston class rating which has limitations which I can't remember off the top of my head (the ones you quote are for the NPPL SSEA not the JAR-PPL SEP - you can certainly do more pax, for example, because a Cherokee 6 comes under the SEP banner), but you could equally well do a JAR-PPL with a Multi-Engine Piston class rating, or a Malibu type rating, or a Jet Provost type rating, or a seaplane rating...
There are limitations on the PPL in terms of size and seating; off the top of my head (and bearing in mind the 10th anniversary of my taking the PPL exams is next year:-) ) they are 5.7 tons MAUM and 12 seats, but you could no doubt look that up... In the States you can put all sorts of weird type ratings on a PPL.
Tim