I'm not calling anybody a liar but I think it is a tolerance thing. I don't believe people who say they don't have any rattles. I've been in plenty of RXs, GSs, ISs, owned 6 myself, and they all have multiple rattles, even demonstrators or loan vehicles with less that 1,000 miles on the clock.
Press any of the trim panels and they all tend to click and creak as multiple hard plastics touch each other - which they do on their own when going over bumps etc. Most of the issues aren't continuous rattles, although I have a couple of those too.
You see hundreds of these sort of complaints on US forums - it is just something associated with Lexus/Toyota vehicles - if you want a reliable car get a Lexus, rattle free then possibly BMW.