Well, you look at it's box office gross (the bigger the box office the bigger the buy), you look at its target audience (family oriented movies generally dominate), you compare it to similar movies (recent genre with similar box office totals and bingo, you have it. Actually it is a little more involved than that but I am not going to give a class, those are the very basics.
Its box office is average, little help there. Its target audience is teens to young adult, a positive thing, they are one of the biggest buying sectors. But did they really connect with that market? I am saying no. I looked at DVD sales for Cap, Thor, and X-men First Class. I took their figures, averaged them, and then doubled them (that could bite me in the ass but I was trying to give the TAS fans a little hope). That put TAS in the 40-50 million dollar range and strongly outperform all recent Marvel movies (excepting the unreleased Avengers).
As I said, the market of 2012 is very different. NO movie (be it the Avengers, The Dark Knight Rises, Twilight, whatever) has any chance of hitting number 1 and damn little chance of cracking the top 10 best selling DVDs.