You're both sort of right. Sometimes a DB with a lot of PD's simply means that he isn't that great, is getting picked on, but still manages to get his hands in front of alot of passes and knock them down.
Most of the time however, a DB (or any position for that matter) with a lot of PD's means that they are simply in good position to make a play. Evidence of this can be seen by the 8 DB's who are currently leading the league in Passes Defensed:
Anthony Henry: 19 PD's
Rashean Mathis: 18
Lito Shepard: 18
Champ Bailey: 17
Chris McAlister: 17
Jonathan Joseph: 17
Asante Samuel: 17
Charles Woodson: 17
Now that is a pretty impressive list of corners and I really don't think that any of these guys fit the category of being picked on by the QB (save for Joseph but only because he's a rook. Also, Joseph by the way has played absolutely stellar this season as proven by his insertion into the starting lineup over Deltha O'Neil).
The poster was right that most DE's get their PD's at the line of scrimmage but that doesn't make their PD any less effective. For anyone other than a DB to have that many PD's is simply amazing. If Taylor doesn't win DPOY this season something is seriously wrong.