There has been talk lately that No. 80 might not be the same player he once was. Ladies and gentlemen, I'm here to tell you that Mr. Johnson is every bit the player he has ever been. As an avid Texans fan, I might be taken as a biased source but being such a fan means I watch the players and see what they do.
There are multiple factors in the, perceived, loss of productivity. Some are things that would eventually happen with any given elite player in a professional sports team. Others can be attributed to team evolution.
A player that has been around for almost a decade cannot escape the film that follows him through the years. Johnson has so much film on him, the inevitable has come to fruition. Coaches have found a way to cover his style of play. It's obvious for anyone who has ever played and/or coached the game that defenses are covering elite players, such as Andre Johnson, in ways that even the greatest would have trouble with. Attacking a player from multiple angles in double and triple coverage will cause a loss of productivity from that player, regardless their elite status.
Another thing to note when wondering about lost productivity is the need to go to someone in double or triple coverage. The Texans offense have evolved into a well rounded system that doesn't rely on any given player or position as they were forced to do in the past. The talent available in the passing game this year is greater than at any given time in the history of the franchise.
Every team expects Johnson to be the main target for the long ball. Thing is, he's is no longer the only field stretcher on the team. Kevin Walter has upped his play making him a greater threat. Now add new young speedsters like Jean, Martin and Posey an you have a field that is not only stretched North/South but also East/West. With everyone expecting the ball to go to Johnson's side of the field, Schaub isn't given much choice but to go to the other side or even go shorter to Daniels, Graham or Casey. Too many options when your best guy is covered like a baby with a king size blanket.
All-in-all, if the Texans want to start helping Andre Johnson get back to the 1100+ yards seasons he's had in the past, they need to stack the opposite side of the field to force loose coverage on their star receiver. If defenses are forced to cover 2 wide outs, a tight end and possibly a halfback on one side of the field, they'll have to leave the star open to cover them.
Summing things up, Andre Johnson obviously still has plenty of gas in the tank, the team just needs to clean the filters so he can run at optimum performance. The man still has another 4 to 5 years before reaching his physical peak.