The length of time to boil water varies all over the map. I am sure your authorities were being overly cautious. My favorite authority, James Wilkerson, MD, in Medicine for Mountaineering, Fourth Edition, states:

"Even though water boils at a lower temperature at higher altitudes, the boiling temperature and the time required to reach that temperature are adequate to kill disease-producing microorganisms, including parasitic cysts, bacteria, and viruses....(Milk is pasteurized by heating it to 160F, or 71 C.)"
p.70-71.

The temperature for pasteurized milk is roughly the boiling point of water on the summit of Everest.

One reason for the longer recommended times for boiling may lie in the circumstance where you are sterilizing cloth for wound dressing. As I understand it, you need to that material for a longer period of time - I have no citations for that concept, however