You can get away with more contact as a DB when you're excellent enough to always be 'in-phase' with the guy you're covering. Revis is the most highly skilled CB in the league at using a variety of techniques, along with being adept at both man and zone concepts. Revis almost never gets 'out-of-phase' with the guy he's covering, which is why he gets away with more.
What he's doing is legal in every level of football, and was in the NFL until these absurd rules slanted towards fantasy football stats were implemented. Being in-phase with the receiver is what allows you to have your receiver covered, but also make plays on the football. If you're caught out-of-phase, you can't make plays on the football because you can't look for it... you have to get back in-phase first, and by that time it's too late in the NFL.
That's why Miami's secondary doesn't force turnovers like they should. The DB's are consistently caught out-of-phase and playing catch up.
You have to maintain some point of contact with your receiver (usually the inside/outside hip depending on leverage) in order to "feel' the routes develope and maintain your 'in-phase' integrity with the receiver.
The primary singular source of coaching tape at almost all DB coaching clinics is Darell Revis, I've seen 'em. Any Coach's Choice or Championship Productions clinics are using Revis as the primary source of teaching cornerback fundamentals. Everything from teaching pattern match concepts (converted zone-to-man) all the way to catch-man techniques uses Revis as the gold standard. He's the true definition of shutdown cornerback in the current era.... even from the slot.
Revis benefits from a reputation he earned, same as Brandon Marshall doesn't benefit from the reputation he earned. Neither reputation was given to either player.
The defensive player is entitled to his space, and on this particular play, Marshall is the one that self-admittedly initiated the contact by trying to use his body, but with poor technique. The refs had no reason to call a flag on Revis...
...and a terrible throw by the quarterback.