Your new job usually offers healthcare to replace your old. True, the coverage can be different - sometimes greatly so. It’s one of the factors you take into account when deciding to change jobs.
Not saying it's not possible to move somewhere sight unseen and without health insurance (since that's presumably what older generations did) but it's still much higher risk than staying put.
There are things like COBRA (http://www.dol.gov/ebsa/faqs/faq-consumer-cobra.html) that help to bridge the gap in coverage.