I didn't think the contact on this play was as flagrant as most of Revis' plays, but he did grab the jersey near the neckline and tug him a little about 15 yards downfield. There was a penalty there but one that often gets missed with any CB.
I think the reason he gets away with this is because he seems to have tremendous arm strength and can affect these recievers with very short bursts of contact. He doesn't latch onto a guy for 3 seconds, but more like 1 second. But he'll do that several times on the same play. He also has good speed even though it doesn't look like it - e.g., way faster than Ty Law was.
The main reason for this INT, however, seemed to be a horrible throw. It looked like Marshall was PO'd on the sideline at the throw.