Okay, I'll take a crack at that...
1. Steve McNair INT: Good coverage and an overthrow.
2. Peyton Manning INT #1: Terrible throw by Manning into good zone coverage. Bad decision that was forced by pressure up front in a game where Manning was already choking.
3. Marvin Harrison fumble: Very nice position on the hit.
4. Peyton Manning INT #2: Another terrible throw and decision by Manning into double coverage.
5. Ben Roethlisberger INT: Rookie QB locked in on his first option and a very bad decision to throw the ball there.
6. Donovan McNabb INT #1: Terrible decision. The ball is thrown into tight double coverage.
7. Donovan McNabb INT #2: Good decision by McNabb, but the throw was too high, causing the ball to fall into Rodney's arms as he was sitting back in what looked to be a Cover-2 shell.
As you can see, a lot of those throws were ones that were forced and were bad decisions. The McNair and Harrison plays were excellent plays that Rodney forced. The others were throws that the QB's forced. When a QB is forced to throw into either double, triple, or just tight coverage, bad things happen. Rodney also had the benefit of playing on a defense where the positions and players around him were stacked. Further, Rodney was known as being somewhat of a liability in coverage. Therefore, QB's typically tried -and thought- they could test him. McCourty isn't known to be nearly as big of a liability. QB's don't throw in his direction as much. That tends to be the case with most highly talented free safeties, as others have pointed out the stats for other Tier 1 FS's in the league already in this thread.