I was one of the lucky ones. My Dexcom was approved by my insurance company without too much hassle. They also covered my pump supplies (including test strips) in full, and I was able to get a new pump before the old one's warranty was up.
That was with my old insurance, which was a PWD's dream insurance. I've since switched jobs, and my new insurance doesn't cover as much. They have a hard time even answering questions about what's covered and what isn't, so I can't report on whether or not my Dexcom sensors are covered.
I'm lucky. Many PWDs don't have the luxury of using the most advanced technology to manage their disease. Their insurance companies don't think it's valuable to have moment-by-moment blood sugar monitoring, to avoid dangerous lows, or coma-inducing highs. Apparently, to many insurance companies, the cost of life saving devices is worth more than the price of a PWD's life.