In the US, healthcare is privatized. So most people have health insurance through their employer, and employers have choices of which companies to use. There are different insurance companies in each region of the country, and a few that cover multiple regions, but none that I know of that offer insurance nationwide, not for healthcare at least. There are also different doctors, hospitals, clinics, etc. that accept these insurance companies. If you switch insurance, you might have to switch doctors.
And then there's the whole issue of pre-existing conditions that might make you ineligible to get insurance (mostly because an insurance company might find covering you too risky, and not profitable). Granted a lot of this is changing due to President Obama's healthcare legislation. But I'll base my explanations on the system as it was in 2011, when my children were diagnosed.
There is government insurance, but it is also state-based, so if you move to a new state, you would have to re-apply, much like from province to province here. And there are lots of rules as to who qualifies. When I was a single mother, my son and I were both covered. At the time we began the diagnosis process, I was unemployed, my husband was in school, and we were low income, so we and both children were covered, minimally, under the state plan.
Our diagnosis process was different for each child. It was a completely different set of events, and a different timeline, than it would have been here in BC. More to come tomorrow.