Most, if not all, of the early face-lift GS300 and GS430 models (X-reg 2000 to Y-reg 2001) didn't come fitted with memory seats. All specifications released by Lexus GB indicated they should be fitted however they also state 'we reserve the right to change specification, equipment and availability without prior notice.'
Maybe a mistake at the factory or shortage of parts, who knows? Lexus official answer is they decided to make a number of vehicles for the UK market without memory seats during this period.
Q&A
Q: Can I convert my car to have memory seats?
A: The drivers door wiring loom contains the wiring that connects to the missing buttons however it is not as simple as just purchasing the button assembly and drilling out the holes in the door trim for the buttons. On vehicles fitted with memory seats the drivers seat contains its own ECU and also position sensors. These are missing from vehicles not fitted with memory seats, there may also be differences with the external mirrors and the drivers door ECU. The cost purchasing and fitted the missing items would be hundreds of pounds.