Why should you be concerned about medical coverage while abroad?  The U.S. State Department lists several reasons:

• The Social Security Medicare Program does not provide coverage for hospital or medical costs outside the United States of America.
• Many health insurance plans do not provide coverage overseas.  Those that provide "customary and reasonable" hospital costs abroad may not pay for your medical evacuation back to the United States which can easily cost $10,000.00 and up depending on your location and medical condition.
• Many foreign doctors and hospitals require payment in cash prior to providing service.
• Uninsured patients may be refused service.
• Countries with socialized medicine may not provide full services to non-residents.
• Payment of hospital and other expenses abroad is the responsibility of the traveler.
• Some countries require tourists to carry accident or travel insurance.

Fortunately, it's possible to purchased U.S.-based medical travel insurance that will cover you globally - including transport and medical evacuation services.  And, while your regular health insurance may not cover you adequately while abroad, medical travel insurance is relatively inexpensive.