Good idea - The owners manual does recommend changing the brake fluid as 60,000 miles as a routine maintenance. The power steering fluid is recommended to be changed at 60,000 miles if you do towing.
I also own a 2008 Ford F250 Crew Cab 4x4 pickup truck. I looked at the f250 maintenance schedule out to 150,000 miles. There is no place that a brake fluid or power steering fluid exchange or flush is recommended. My f250 4 wheel drive pickup truck weighs 8,000 lbs. You would think between a Lexus ES350 and an 8,000 lb pickup truck that it would not be the Lexus only that recommended these items? Then the Lexus brake and power steering systems are inferior to the Ford? I would not think so. I thought the Lexus vehicles were superior to most others. I guess not.