I think Jessica uses singles as a warmup at Nationals, and, since she's done both events since skating at the Pre-Novice leve (similar to American Intermediate), she's always had two things to think about, instead of only pairs. I think it's her way of dealing with the pressure, and I think she said something about that in an interview at Nationals 2007, after her SP.
Either way, nice article, and I wish them all the best at Worlds!
Kypma