In California, a situation between a county search and rescue service and a private air ambulance is similar to what's going on in Maryland.
In Ventura County, California, the Sheriff Department operates a helicopter that does rescue and on-scene work. At least one private service (Mercy Air) contends that they can provide on-scene service less expensively. The article below highlights one incident that has gotten the local media's attention.
Air ambulance ordered to leave fatal crash scene - Ventura County Star
http://www.flightweb.com/article.php?story=20030327025841723