Does one mission statement really cover the motivations of a company that has branched out into so many areas? Reader is a huge blow to that mission.
In itself, Reader could fit in (as the article by one of the original developers touched on). But for various reasons they never worked this out, or didn't put enough resources on it. So now they pull the plug. A stupid decision for many reasons, but not necessarily from a purely 'strategic' point of view.
One reason I can think of that they never invested deeply in Reader could be that the subset of people using it actively (geeks, information addicts) just wasn't interesting and broad enough to them.