In 2005, Hyundai subsidiary Kia Motors also replaced its CEO with a Korean executive.
From here, it looks like Hyundai wanted to improve communications with corporate headquarters in Korea, and perhaps to tighten corporate control of North American operations.
Cosmai has been CEO since 2003. He joined Hyundai in 1998 as Vice President of Sales. Since Cosmai joined the company, annual sales have rocketed from 90,000 units to a forecast 500,000 units in 2006.