Federal regulators formally approved the merger of the nation's only two satellite radio operators yesterday, ending a 16-month-long drama.Sirius Satellite Radio Inc.'s $3.3-billion (U.S.) buyout of rival XM Satellite Radio Holdings Inc. will mean 18 million-plus subscribers will be able to receive programming from both services. Executives say it will mean huge cost savings that will lead to a first-ever profit for the relatively nascent industry. ...