Haven't changed a brake pipe in years, but i've always kept the exposed brake pipes covered in grease and the same goes for any other exposed pipes made of material that corrodes.
They are prone to corroding on many cars, in most cases if deteriorating they get picked up on the annual MOT so its not something one should be too worried about.
In my experience its the brake pipes that link the rear brakes together that can leak, often they go over the top of the rear suspension and are really difficult to see and can be equally difficult to replace, i suspect the rear pipe(s) on your Lexus would be far more difficult to replace than on the LC, but if you get the vehicle serviced at a competent garage i would expect them to be keeping an eye on such things for you.
Thinking further it's more than likely that the entire underside of the Lexus is covered in plastic undertrays, meaning things are protected more but also makes inspections harder, if the Lexus were mine (and yes i'd love a LS460 or GS450h) the only pipes i'd be thinking about checking carefully due to normally being hidden would be the long front to rear jobbie and the section(s) that cross over the rear suspension if the car has that design.
On my W124 Merc the corrode point for the rear brake crossover pipe is where it sits under the small rubber insulated clips, salt gets trapped in there, no doubt vibration plays its part here and they can corrode at those points even if you do spray them with grease etc, its those rear pipes that tend to start leaking in my experience because they are so difficult to inspect and replace compared to the rest which are an easy check for the MOT inspector.
Last time i changed a brake pipe didn't go OE but got them made up of 'Kunifer' alloy which didn't corrode, but that was many years ago and for all i know there might now be some other go to material.
Course its all very well greasing the brake pipes etc but that will go down as an MOT advisory, my MOT's always state chassis etc covered in grease or underseal or whatever too, those advisories wouldn't probably worry anyone here quite the opposite they'd be happy seeing them knowing someone's looked after the motor, but lets be honest people here arn't exactly normal in the world of motoring (no offence people but we arn't), but for a vehicle like your Lexus potential buyers may not appreciate in the same way.