Are winter tires really necessary?

Judging by the tone of your question, I don't think you are really asking whether winter tires are necessary but rather your using your own experience to justify why they are not.  Can you get by a Michigan winter on all-season tires?  Yes.  Can you benefit from using winter tires compared to all-season tires?  Yes.  

I can think of 2 separate instances over the years where I am certain I was able to avoid spinning off into a ditch, guardrail, and/or striking another vehicle because my vehicle had winter tires.  The price of the additional tires was far less than the cost would have been to repair my vehicle due to a collision, not to mention the inevitable increase in my insurance premiums.

As a small side note, my insurance company also gives me a discount because I use winter tires.  It doesn't offset the cost of the tires but it helps a little...

not in LA    

Driving a vehicle with Blizzak Winter Tires is great if you can afford winter tires. I just put a set of Blizzak WS 90's on my Bonneville and you wouldn't be able to keep up with me in your AWD Traverse in the snow!

They're not absolutely necessary, but they help.

A master craftsman could probably build a good house with lousy tools, but they could build a better house and do it faster if they had good tools.

You can probably do "just fine" with all season tires on your AWD vehicle, but you'd do even better with true winter tires.

You know how to drive in cold, most people do not.  They have been told to used crutches, AWD and Winter Tires; and have never learned how to drive in the cold.

If you are not willing to learn how to drive, winter tires are necessary.

Winter tires are better than all season tires. But they are not necessary.

For the past 30 years, I have put matched Studded Tyres on ALL four of my 2wd and 4wd vehicles, each winter (Nov to Apr. by law in my state). The little bit of extra traction has always made driving (and STOPPING) much easier on Snow and more importantly on soft  Iced roadways.

I even have an extra 4 wheels to keep the balanced tyres ready for easy swap over.

Balanced once reduced expense of balancing, and less chance of damage of changing the tyres from rim to rim twice a year. 

The cost of the extra rims is easily covered by the lack of need to balance them twice a year.