Ten years? Just kidding!
One of the things a number of conservative in the US have admitted to doing is deliberately taking extreme positions on issues not because that's what they believe, but in order to shift the "centre" of the debate rightward. If Hillier says 2017 and the current mission is set to be done in 2009, all of sudden 2011 looks less like a questionable extension of a mission about which many remain skeptical and more like a nice compromise position.
Maybe I'm being too cynical, but it appears that thus far Hillier seems to be able to get what he wants and he's used the media to do so rather often. I don't think this is beyond him.