I think you're right and reason it makes sense is because your body is working in conjunction and when you "separate" the 2 halves incorrectly it leads to bad results. For example if you're fooled by a breaking ball you might end up twisting your hips prematurely while leaving your upper body motionless thus throwing off your balance, probably rolling over the ball, and depleting your power. Keeping them all in sync is key to consistent hitting.

To explain exactly what he said in the article:

"The main thing right there is that he started separating better. When you start separating better, that's everything you're doing before your swing. That gives you a chance to see the ball better. Besides taking some length out of your swing by separating on top, that gets you to stay square as we put it. When you're square, you're seeing the release point with both eyes and not just your lead eye."

When he says "separating better"- the correct way to swing is to rotate your lower half along with your back pivot foot and then turning your shoulders parallel to the pitcher. That would be the separation. This is all done before you even begin to swing like he said.

What he means by "squaring up" is having your chest facing the pitcher thus keeping you balanced and allowing you to see with both eyes like he said. If you don't turn your shoulders and "separate", you probably will end up leaning over the plate for outside pitches and you will only be able to see with your lead eye.

Finally, the reason he says separating will shorten your swing is because if you don't turn your shoulders pre-swing, inevitably you will be swinging with your wrists back and it takes longer to get to the ball. When you rotate your shoulders before you swing, the bottom of your hand should start towards the direction of the ball cutting the swing down (because all you have to do to swing is then use your wrists to guide the bat), and improving your accuracy. Guys with long swings (Sexson) have trouble hitting for average because obviously they have a longer way to go to hit the ball and are truly kind of guessing more.

Basically watch Barry Bonds in slow motion- he does this all to perfection. Hope that clears it up.