Dear Mike/Alan,
Indeed the LS 430 was the first Lexus configuration to have the soft close (or power) door/trunk options both in the US and UK markets (it may be that some earlier Toyota Celsiors sold in Japan might have had this option before 2001 but I am doubtful on this). The 2000 model year LS400 is distinguished by Brake Assist and Automatic Folding Mirrors.
The soft close doors were options included only on the Premium Pack models for 2000-2003 (spanning 2001-3 model years)on UK cars, and the Ultra and Custom Luxury versions sold in the US market. From October 2003 on the UK facelift models had the soft close options as standard - indeed the only differentiating option being the Automantic Cruise Control (ACC) / Pre Collision System (PCS),other than colours, wheels and interior trim etc. In the US there were 4 main specifications of car; the top being the Ultra Luxury (everything including Radar Based Cruise Control with PCS, Nappa Ecru Leather and grey ed wooded veneer trim) and Custom Luxury (different laser-guided cruise control, sonar-based Intuitive Parking Assist, DVD navigation system , air suspension, power door closers headlight wash , but not PCS) Note in the US the standard car did have a power trunk/boot closer, but not even Sat Nav/ Mark Levinson sound system which came only as part of the optional upgrade from the standard car known as the Modern Luxury Package inc Bluetooth etc) but even this did not have Air Suspension but springs!
Trust this helps,
Richard