Apple is usually very protective of their intellectual property, so they're probably pretty pissed that a trademark officer rejected their application to own the phrase "iPad Mini." They wield patents like lightsabers and are not afraid to chop off the hands of people they feel are infringing on their intellectual empire. But the United States Patent and Trademark Office's reviewing attorney didn't think Apple made enough of a case to own the "mini" name.
Patently Apple discovered Apple's rejection letter was just released over the last few days, even though Apple was informed of the denial on January 24, 2013. There's no reason provided for the delay releasing the letter, but we do know why Apple was denied the trademark: "the applied-for mark merely describes a feature or characteristic of applicant’s goods," the reviewer writes. The USPTO attorney makes the case that the iPad mini doesn't have a "a unitary mark with a unique, incongruous, or otherwise nondescriptive meaning in relation to the goods and/or services." It's just small, he says.
Additionally, Apple usually forwards their product website address instead of providing "a specimen," in this case a real life iPad Mini, with their application. But this reviewer didn't appreciate that and said as much in his rejection letter.