I'm sorry to say this,but I do think that leading up to the film,Ledger's death was on the minds of alot of people. I can remember being in line at the store and hearing people talking about The Dark Knight just behind me. Now,these were girls who looked maybe 19,20 years old? I mean,you knew that had no real interest in Batman or comic books but they went on and on about Heath and his death and how they will be seeing TDK. So,you know that his death brought alot of people to the movie that wouldn't have gone before. However,I think that all the positive reviews did it as well(and the great reviews of Heath's performance). As I've mentioned before,the movie is epic and a masterpiece. It's become an "event" movie that everyone has to see.
Now,I think that Spider-man 3 should've been that same kind of film,and it was for the first week or two. Everyone,and I mean EVERYONE, was looking forward to black suit Spidey and the appearance of Venom. I mean,Venom isn't Spidey's most dangerous and popular foe for nothing! People and fans wanted to see him. I can honestly say that I've never looked more forward to a film in my life,before or since. From the trailers and pics this film looked to be a very dark film and many(including myself)was REALLY looking forward to the Spider-man vs. Venom fight that we all thought would happen. That's exactly why the movie broke so many records that first weekend. But,I think when people saw it and saw how crowded the movie was,and how little Venom was in it,then they spread the word and even though the film recieved more positive then negative reviews,more people tend to listen to the negative than anything else(don't ask me why). And fewer people went with each passing day. The film was the highest grossing movie worldwide in the franchise's history,but when you have an opening weekend of $150 million,your final gross should be alot more than $325-30 million(here in the states). I believe that word of mouth brought the movie down a bit.
Now,all that being said,I really don't think that TDK's success will have a huge impact on Spider-man 4. I think that all films will look at little things The Dark Knight did and try to fit them into their own movies,but the Spider-man franchise is the most successful superhero series ever created. The first two films were awesome and the 3rd film,while not reaching the great heights people expected,is still a great movie and a nice addition to the franchise. But obviously,alot of people found it disappointing. So,if anything will effect what happens in Spider-man 4,it will be Spider-man 3.