The main attractions were also mainly action movies. One (although I forget the title) starred Michael Cera and was clearly intended for more of a high school audience. In the trailer, the main character falls in love with this girl who is mysterious, and has many ex-boyfriends who all want her back (not much else is clear, other than that this predicament leads to a lot of action sequences). Another trailer was for the movie 'Due Date'; it stars Robert Downey Jr and Zach Galifianakis, and is a road-trip action/adventure comedy very similar to 'The Hangover'. This was probably included because much of the audience of 'Inception' is teenagers/young adults, and movies like 'Due Date' are targeted toward that age group.
The last trailer, 'The Town' was a crime movie about Boston gang activity (with a bit of a spooky mood similar to 'The Dark Knight' - many of the villains are masked similarly to the joker). This also falls into the action category, and is a bit mysterious like 'Inception', which is probably why they included it as a trailer.