Sorry, but you're just wrong. I'm almost 100% certain they play cover 2 more than any other scheme. And there's an easy way to settle it - watch the games and pay attention to DB play. If the CB's are in the flats (under ~15 yds) it's cover 2, and if Sash is in a flat it's most often cover 3 (Hyde and Prater outside 1/3's and Greenwood middle 1/3). Greenwood is pretty much always either deep 1/2 or deep middle 1/3, which is why you don't hear much about him making many tackles. (The other reason you hear so little about Greenwood is b/c he's almost always in his proper zone and doesn't blow coverages.) IA almost always plays 2 deep, 5 under or 3 deep, 4 under. The thing is the CB's often play deeper in their flat coverages, so they give up the under stuff much of the game.
Think about it schematically - if they were always in quarters coverage, that would be only the 3 LB's underneath. Any pass D scheme designed in that manner is destined to fail (unless it's a Hail Mary situation). And in cover 2 the CB's may run deeper w/ WR's, but that's just dropping into coverage in their deeper flat zones (up to ~15 yds), not playing a deep 1/4. DB's are also trained to react and run to the ball as soon as it's in the air, so on any deep throws they'll be moving and if the ball hangs up long enough they'll chase it to make it look like they're in different coverages - think the late dropped OSU deep ball Sat. Greenwood and Prater end up about as close to Posey as Sash did, who should've been in that coverage.