Good question and I think the answers are somewhat visible given what the defense evolved to with Aqib Talib in 2012. To really get a sense of the shift we need to go back to the late 2000’s.
Here’s the Pats D vs. Colts 2009.
At the snap, the undersized corners (Wilhite and Bodden) will turn and run. The Pats have a third safety on the field to cover Dallas Clark.
Here’s the Pats D vs. Broncos in 2013 AFCCG.
Now the corners attempt to jam and disrupt the timing right at the line of scrimmage. You can just tell by the difference in the corners presnap stances that they’re playing a different technique now - they’re lower, ready for contact, whereas before they’re getting ready to turn and run.
So that, in essence, is really what it is all about. The late-2000’s Pats were content to play more zone coverage and to use what they perceived as athletic and smart corners who could pattern-read and jump routes.
Asante Samuel was the perfect example of that kind of corner.
Whether it was quarterbacks getting too good or the rules allowing no contact downfield (or a little of both), zone coverage became easier and easier to pick apart. There’s still a place for zone coverage, you have to mix-and-match, but to play mostly zone will result in giving up more passing yardage than anyone else (like they did from 2010-2013).
Now you must take your chance to be physical with the wide receivers when you can be - within five yards of the line of scrimmage. That disrupts the timing of the offense and buys that extra second for the pass rush.
That also doesn’t mean that just because you’re pressing you have to play man. The Seahawks will press and then drop their corners into cover three.
What Revis and Browner (and Dennard and Arrington and Ryan to other extents) allow the Pats to do is to win at the line of scrimmage.
If only we could stand Revis/Browner side-by-side to Samuel/Hobbs. That picture would be worth a thousand words.