Hi ZeeRX350,
I can't speak to whatever book your mechanic was looking at, but Lexus recommends that you change the oil at 1,000 miles, at 5,000 miles and then at 5,000 mile intervals. And since Lexus provides the 1,000 mile and the 5,000 mile service at no charge, why wouldn't you? Your mechanic will charge you for it.
Also, at the 1,000 mile service, they will program any 'personal setting' changes you request (see your user manual). At the 5,000 mile service, they will inspect the brakes and rotate the tires. Both are good things to do on a regular basis- especially if its free!