It took me a long time to find out that the IS300 2JZ-GE is _NOT_ an interference engine. Many, Many Lexus people told me that it was, but Lexus Canada talked to the engineers in Japan and gave me an official answer of "NON INTERFERENCE" engine.
With my old MR2, I think 60K was recommended, but many people would stretch out to 120K before changing it. Even though your engine shouldn't be damaged if it breaks, you would loose all power, which can be a dangerous situation if you are in traffic. At least my MR2 with manual trans, and manual steering is reasonably "coastable" if power is lost. The much heavier IS300 with auto trans and power steering could be very ungainly to drive if the engine completely cut out on you.
Many other Lexus engines _ARE_ inteference design, so it may explain why many Lexus people assume that the IS300 must be too.
Also, some may say that it IS (interference) just to scare you into changing the belt at the recommended interval.
Most BMWs use a chain rather than a belt which does last alot longer.
Lexus probably went with a belt because it is more quiet, and costs less.