I don't think this is actually true. The software supports a very rudimentary type of "pressure sensitivity" that (i think) is based on the capacitive area of the rubber tip. Maybe this can still be considered "active?" Perhaps. It is my understanding that the ability to determine the size of a touch (a radius?) is a system-wide thing that was added for iOS 8.
In practice, there is a huge difference between a true pressure sensitive stylus, i.e. a wacom stylus, with, say 1024 real levels of sensitivity, versus this more kludgy solution. The Wacom solution is far closer to real media performance. Paper, when used with Pencil seems to support 2 size variables. The first (mentioned above) is based on the new iOS 8 size of the rubber tip deal. The second size variant is based on the velocity that you use to draw your line. The faster you draw, the fatter the line gets. Amusingly, this is somewhat backwards of the way a real artist would use a brush loaded with, say, India ink (like an inker would use). In that scenario, the faster you move your brush, the thinner your line is (generally -- artists can vary this greatly with practice and technique)
Anyway, this Paper and Pencil deal has vastly improved since the first version. The tracking, the connection to the Pencil -- all have improved dramatically. Highly recommended for iPad artists and non-artists.
One thing to note is that a newer iPad will be much better at tracking than an older one (obviously!).
Only thing I'd add is that because of the carpenter pencil shape of the Pencil, the contact area "pressure sensitivity" seems to work well if you're using the side of the Pencil to shade an area with the software pencil tool, as one would do with a real wood and lead pencil. Outside of that one example, I don't find that the "pressure sensitivity" contributes anything.
