I just wanted to make this post because this idea was really popular months ago, and I saw a different post about this on the forum.
Here is the original paper: http://www.ncbi.nlm.nih.gov/pubmed/19346988
It seems tempting to conclude that standing up leads to living longer, but that would be the same as eating vegetables leads to obesity (http://www.nature.com/ijo/journal/v32/n6/abs/ijo200821a.html
), or obesity leads to diabetes. It's only a correlation, and it's easily possible that standing up and living longer are caused by the same thing.
One cause linked to both would be insulin sensitivity. Insulin sensitivity is linked with longevity. Gary Taubes also talks about how diets make you more inclined to be active, with the implication that eating more while being insulin sensitive would cause your body to be inclined to be more active.
Something to think about before getting a stand up desk.