For clarity here is the information I have received from Lexus re satnav update:
all Lexus models come with a 3 year licence (used to be 1 year)
when expired you buy a new licence and are then able to download updates (usually twice yearly)
a new 1 year licence costs £175.40 - includes updates
a new 3 year licence costs £280 - includes updates
the questions were answered in relation to an LC500, but may apply to all models