Sort of. There's really two problems here that get confused.

1) Who is this file about? An XML head will look at most FOAF and think it's obvious because there's only one primary person in the file. PPD is about making this explicit in the RDF triples. "This document is about this person with this nodeid". This matters to people building aggregators because they want to say "This person and their profile is described by these foaf files". Without the explicit PPD information it's very difficult to do any more than list every file where the person appears which could be hundreds or thousands if you include all the places where they appear in a knows relation or there's a bit of FOAF at the top of an RSS feed or suchlike.

2) Who wrote the data and hence can I trust it? To do this properly involves PKI and irrefutable signing of foaf files. For people like Tribe and Ecademy this is a pain to implement and we can only sign the data with our own signature not the user's. But what we can do is to provide a couple of pointers in the file as to where the data we're including came from.
1) The Generator code. We can probably trust data coming from SNs or other systems that validate users, have T&Cs and authenticate with logins. Hence <generatorAgent /> and
<errorReportsTo />
2) Elements in the file that says this Person with this NodeID entered the data. This is the foaf:made and foaf:maker elements. Without signing, we can't be sure this is true, but if we add it to "and this is where we found the data" we've got the beginnings of an audit trail.

Bug! The ? mark is being treated as an end of url char.
www.ecademy.com/module.php ? mod=network&op=foafrdf&uid=1