I don't really get the point of having a "second bonnet" - there is already one covering the engine and everything else.

Lexus has been known to make things deliberately difficult to reach, like putting the starter motor in a place where getting to it involves disassembling most of what's on top of the engine (requiring the replacement of lots of auxillary "soft" parts like gaskets and o-rings in the process):

http://www.lextreme.com/starter.html

In comparison, most other makes and models mount the starter motor somewhere on the side of the engine or transmission where getting to it doesn't require disassembling much else.