I hiked, climbed and worked outdoors in western Washington for over 30 years. I think I can claim at least a full year and a half of camping out throughout the year there at all elevations, in all weather and undertaking many different pursuits. In addition, I spent six months on a field research expedition in Antarctica. I think I have a pretty good idea of the various flavors of cold weather.

My experience in the Cascades includes winter ascents of Mt. Rainier, Mt. Hood, Glacier Peak, Mt. Shuksan, Mt. Stuart, Mt. Baker and many less well-known summits. I have had to deal with hypothermia as a "first responder" on eight separate occasions; mostly in the summer and with parties other than my own (dayhikers) and with two exceptions, below 3000'. Why did the hypothermia occur? Because the individuals were not prepared for the wet and cold and when they started to deteriorate, they, and others in their party, lacked the warm clothing and shelter necessary to reverse the situation. Two of the people died.

You seem more than a little bit cavalier about the conditions one might encounter in the Washington Cascades. I suspect that this results from inexperience. Mark Twain once said "the coldest winter I ever experienced was a summer in San Fransisco". He was referring to the cold, damp, sunless weather that can inflict the Bay area in summer. The Cascades, especially above timberline, can be like the Bay area in spades. You may not have encountered bad weather on your summer trips there but if you keep going, you will. If you do, I hope that you will be better prepared than you appear to think necessary. Any outdoor endeavor is best approached with humility, not hubris.

I guess I don't really care that much what the American Alpine Institute in Bellingham recommends for their pampered clients; to me it sounds like a lawsuit waiting to happen. I suspect that Jimshaw alone has more outdoor experience than the collective experience of their entire staff.

You cite a lapse rate of one and a half degrees per thousand feet for the maritime Cascades. That is about right. The reason for the low lapse rate is that water making the transition from vapor to liquid releases heat. This is what keeps the temperature drop low; it also results in a lot of rain on the western slopes. Most hypothermia deaths occur at temperatures above freezing with high humidity, wind and rain; conditions that are not that uncommon in July and August in the Washington Cascades.