I bought the Blu-Ray, HT figures, even Hasbro figures from it but that's because I'm an Iron Man fan and not because the film was good, Iron Man 2 was one of the weakest films in that genre considering it's original source and the fact that most of the original team was still intact.
The same reason that I have a Green Lantern film Power Battery, the Mattel figures, T-shirts, a custom film Ring and will buy the HT figures because I'm a fan of GL not because that film could be considered good. Fandom of the character still saves over the quality of the film, look at Spider-Man 3 merchandise or X-Men: Origins Wolverine figures where the films were duds and forgettable yet the character love is there.
Marvel has been working towards The Avengers since 2008. A project in the process for 5 years and given that Iron Man was in preproduction since 1997, who knows when the whole Avengers thing came to pass maybe longer.
That is a lot of pressure and a lot riding on this to work. The best scenes in the film CANNOT be them sitting around the Helicarrier teasing each other about shortcomings. This thing has to almost be Bay-like in it's over the top action mixed with the general Marvel humor or it'll be considered questionable. Not to mention with so many characters both hero and villain packed in, this is already heading into "trilogy" waters where it's previous examples are things like Batman & Robin (a fourth film in reality), Spider-Man 3 and X3 where it was so overloaded that the story suffered beyond repair.
There are a ton of red flags already up on this and if it works it'll really be something special and if it fails it'll be one for the record books but the merchandise? It'll sell without a doubt and people will buy it on DVD/Blu-Ray
because comic fans are gluttons for punishment, why do you think people own copies of Ang Lee's Hulk, The Punisher, Fantastic Four or Daredevil? 
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