@bonanova: You're right that if the wind direction has both head/tail component and cross component relative to the trajectory then analyzing only one or the other will result in correct conclusion that wind adds to travel time. However, the only crucial fact that I was trying to show in my previous post was that there exist closed paths (i.e. straight line A->B and back) and wind directions (i.e. perpendicular to the path) for which ignoring the cross wind component will result in incorrect conclusion - same time with and without wind. In other words, in some cases, the entire time penalty is swept under the rug.