I assume you're referencing the play at 13:25 in the link in your last post. It's certainly an issue on that play.
I disagree with the commentary that he needed to lay out for the ball. He did not extend his arms and the ball went off his finger tips. He just misjudged the ball. We see the same thing in my last post where he misjudged the ball on the punt return. I don't see the issue as one of concentration; it looks like he just has trouble tracking the ball. He should get a thorough eye exam. He won't be returning punts if continues to misjudge "fly balls".
Much has made of his 16 drops and 3 fumbles over the last 3 seasons.
For perspective, one of those fumbles, I presume, was on that punt return. I count 237 touches receiving, running and returning over the past 3 years. That would be 1.3% fumble rate per touch. That's high, but the sample is small. Scratch the punt return, subtract one fumble as perhaps an oddity, and the ratio is relatively small.
As for the 16 drops over 3 years, I don't know the target numbers for those years, but I seem to recall 2014's number was 94 give or take. Assuming the 94 and his target-to-catch ratio being the same for the 3 years as it was last season (65%), then one arrives at something like 230 targets and a 7% drop rate.
If that 7% drop rate is reasonably close, it's a bit higher than one would like but not particularly troublesome.
According to McGuin, using presumably the Packers coaches' scoring, Cobb's career drop rate is 6.27% and Nelson's is 5.64%. A 1.0 - 1.5% difference in drop rate is nearly indistinguishable over the course of the season unless a guy drops a game winner that gets burned into the minds of fans.
http://www.jsonline.com/sports/pack...andall-cobb-leaves-b99455123z1-294947891.html
Again, tracking the "high fly" seems to be the main issue here.