I can't imagine why any reader would be disapointed that Snape is not a pure-blood. If possible it makes him even MORE facinating to me! Incidentally I saw someone yesterday on FAP who felt let down and disapointed that Snape didn't have a nice, big house! I know, I know, I shouldn't go there because I always end up coming back to lj and complaining about it...

This discussion about blood and how important it is shows me one thing though. I find it inconceivable, at this late stage, that JKR will be able to answer all of our questions in book 7. In a way I'm quite glad of that as I think it will give the fandom a longer lease of life to have grey areas to ponder and discuss.