We all know that Djokovic has got excellent defensive, and defence to offense skills. Djokovic's game revolves around returning every ball as long as he can, forcing his opponent to go closer and closer to the line, or to approach the net with terrible approach shots. If Djokovic manages to put his opponents in a defensive position, he often chooses to slap a winner in the court. Really effective.
I agree insofar that Djokovic's natural tendency is to grind points out, but I disagree with the notion that he's offensive only "if he manages to put his opponents in a defensive position". He takes initiative much more than you're giving him credit for, even if it's not always by way of an outright bullet. He moves the ball around the court with seemingly little effort, and that greatly facilitates his ability to displace his opponent and step into the court.
Why do most of the opponents choose to attack Djokovic's almost inpenetrable defence? In my opinion (once again, Im not a professional tennis player, easier said than done) if you choose to grind Djokovic down and simply move him from side to side with no pace balls, Djokovic will eventually lose his temper and try to go for winners, which he doesnt do well.
You certainly shouldn't just try to redline it against him. But rather than junk balling him, I've always felt that the trick is to give him plenty of variety. Alternate pace, spins, and placement; take chances. He's a textbook baseliner, so the last thing you want is for him to get "used" to anything. One of the reasons I think he played Nadal so effectively last year is because Rafa generally gives you the same ball from the back court. To his credit, it's more than enough to grind down or muscle through most of his opponents, but Novak got a handle on it and Rafa didn't have the variety to upset him.
Ive seen this many times in the past, and more recently Federer at Wimbledon.
"In the past" really refers to pre-'11 Nole. As someone capable of both extensive offense and defense, he used to have a real problem with balancing the two playing styles. This caused him to both get trigger happy and fall into defensive ruts at times, but he's become a lot more constructive and even-keeled in the past couple of years.
When it comes to Wimbledon, you have to keep in mind that Novak is simply not a great grass court player. More particularly, his movement on the surface just isn't comparable to the other top players. Federer got the ball behind him a lot in a way that probably wouldn't have worked on other surfaces, where Djokovic's movement is outstanding. Roger used experience and grass expertise to keep Djokovic from getting behind the ball, but that's no precept for playing him.