You've got to distinguish between centre clearances, where numbers are always even, and clearances from other stoppages around the ground, where generally they are not. For stoppages away from the centre square, we will generally allow the opposition a + 1, while our spare player will be behind the ball. Our wager is that enabling the intercept mark behind the ball will more than make up for any advatnge they get from winning clearance at the stoppage, particularly given the quality we've got in the ruck and around the ball means we think this advantege will be minimised across a game.
When we get beaten out of the centre, the explanation has varied, I think. If we're not just getting outplayed there (like last night), the opposition has done their homework and operate on the basis that Gawn and Grundy will win most hitouts, and set up accordingly.
I still reckon our rucks should often just belt the ball forward, allowing our mids to swarm in that direction, Clark Keating style.