Water temperature will not exceed it's boiling point unless under pressure; the boiling point drops as atmospheric pressure drops (e.g. when hiking/camping in high mountains).

I too have heard, "big bubbles, no troubles." The article at http://www.survivaltopics.com/survival/how-long-do-you-need-to-boil-water/ seems to bear this out.

In an urban survival situation, boiling is a dang good idea, although it won't remove chemical pollutants, heavy metals, etc.

In wilderness areas in North America, the water is generally safe to drink without treatment. The majority of girardia cases are generally caused by poor hygiene. Yes, this isn't what is generally accepted, but I've read the studies. However, having read the studies, I continue to treat my water. The cost of treatment is low, but the consequences of being wrong are high -- particularly in a survival situation. My point is this: hygiene, particularly hand washing, is as or more important as/than water treatment.