Rudy,
Real-world requirements are rarely complete, and the Developer assignment certainly tests the programmer's ability to make sound judgements in the absence of absolutely complete specifications. One criterion for such judgement is whether the system produced exceeds the client's requirements - no client is going to be happy paying for functionality he didn't ask for. You'll find plenty of occasions during the assignment to invoke the paragraph you quoted and make design decisions without going beyond the functionality required by the instructions.
I've corresponded with several people who've completed the exam and earned their certification. Some of them have produced the bare minimum required and some have gone a bit further, but I've never heard of anyone going to the lengths you suggest.
That said, my own design exceeds the requirements in a couple of minor ways (and now that I'm
testing and debugging the server side, I'm considering trimming it back somewhat.) Build what you think is the right system, but remember that Sun doesn't award extra points for going beyond the requirements.
Jerry