Inspired by the location of the memory seat control panel in RX300 and the similarity in contruction between RX300 and IS300 (for instance, the window frames, door handle), it may not be that technically expensive for Lexus to provide this feature in IS300.
The memory seat control panel for RX300 is located on the left hand side on the dash besides the steering wheel.
So I would think that the switch place where there is a coin-holder could be used for the memory function.
Of all the possible options, memory seats are near the bottom of the list. If I was married and my wife was driving the car 50% of the time, then I can see the need for memory seats. I will drive the car 99% of the time, so I see no need.