Do you guys really think some purple is going to make that much of a difference? It won't affect the movie all that much. My main concern design-wise is the face.
Well yeah, you're right it's probably not gonna make a huge difference. But from what I learned in my marketing course (which is actually not much

), a company should always try their best to satisfy their consumers. In this case, adding some purple to the costume probably won't hurt very much.
Of course, fanboys make a small percentage of the general audience (like what, 10%?). It's pretty obvious that the target audience is not JUST fan boys, but also people who are watching super hero movies now. but that 10% could mean 4.4 million dollars of gross profit to the company (according to wiki, it grossed 40.4mil in August 2012). I really don't think adding some purple would be that hard. Some fans would boycott the movie because of the lack of homage to the comics.
Some people boycotted the first one because the costume was different. I personally, would never do it. But there are people like that out there and it won't hurt for Sony to just appeal to them every now and then, especially when it comes to an important character like the Green Goblin
EDIT: but yeah, you're completely right. My main concern was the face, until I saw the poster. I have no complaints there.