Unanswered Dursley Questions

[Joe Bento]

The Half-Blood Prince was certainly a shocker, adding as many 
questions to the queue as were answered.

Am I the only one that wished there was a bit more dialog about the 
Dursleys - Petunia in particular.  Back in OotP, when Harry arrives 
home with Dudley following the Dementor attack, Petunia dropped the 
bomb when Vernon asked what the ruddy hell dememtors were.  Petunia 
blurts out that they guard the wizard prison, Azkaban.  Harry was 
obviously as shocked by this statement as learning Mrs Figg was a 
witch.

For someone who hates the wizarding world as much as the Dursleys, 
that's a rather trivial piece of information to retain for so many 
years.

Do we just accept the fact that Petunia has some basic understanding 
of the wizarding world because her sister was a witch, or is there 
more to this woman than we've been led to believe?

I'm also trying to understand Dumbledore's statement of how 
important it is that Harry return to Number 4 Privet drive before he 
comes of age.  Is this to protect Harry, or the Dursleys?  When 
Harry does come of age, the protection spell apparently no longer 
works.  What danger does this put the Dursleys in?

Two years or so is certainly going to be a long wait!

Joe