Checking some of the references in Google again it's obvious Raewyn is primarily a New Zealand name. Many of the Australian references turn out not to have been born in Australia. For example, the Australian children's author Raewyn Caisley was born in New Zealand, and the fertility specialist Dr. Raewyn
Tierney lives in
Sydney but received her undergraduate degree from Auckland University. The prominent Australian sociologist Dr. Raewyn
Connell is a transgender person who was born
Robert William Connell, and so chose Raewyn on her own as an adult. So I guess the American references to Raewyn as an "Australian" name are the result of people not paying enough attention to the difference between Australia and New Zealand. :)