Welcome to life with a torquey RWD. This isn't a Lexus thing, it's a combi of lack of wet driving skills, vehicle weight and tire performance. I lived in SoCal for a year, coming from Massachusetts, and folks out there don't have the slightest idea how to drive in the wet. As stated by 54406, your tire type, condition, inflation pressure all have a big impact on how your car is going to handle in the rain. If you're running all-seasons, guess what...all seasons suck at driving in ALL seasons. High-performance tires vary widely in their wet performance. A great dry road tire may handle terribly in the rain.
Next time it rains there, I'd highly recommend taking your car out into a big abandoned parking lot and finding out what the limits of your tires and the car are. Learning what the car feels like before it's going to break loose can save you from future problems. I practice my snow-handling skills in my SC300 regularly. I took it out driving despite the blizzard yesterday with no problems.
