Pop music icon Elton John announced Thursday he is cancelling a trio of scheduled Las Vegas performances on doctor's advice after being hospitalized last week for a respiratory infection.  A spokesman for the Caesar's Palace Casino confirmed that the singer's performances on Thursday, Saturday and Sunday have been cancelled.  The singer was admitted to Cedars-Sinai hospital in LA on Wednesday, where he was treated and released.  Doctors recommended that Sir John take a week off from performing and prescribed a regimen of antibiotics.  The canceled shows are part of John's "Million Dollar Piano" show, a three year residency that began in September.