Why did Rowling intend to kill Arthur in book five?

[potioncat]

No: HPFGUIDX 180417

"Catlady wrote:
snip
Snape appears to be making a point of deceiving without actually lying. 
On  one paw, Snape has to be a good liar to survive his double-agent 
role for even minutes. On another, has he ever outright lied to Harry? 
I wonder why?


Potioncat: He's also adamant that Harry not use Dark curses. I don't 
think we ever see Snape use Dark Magic either. (Except the cutting 
curse on James, and whatever he did to Wormtail in the stairway)

Back to deceiving without actually lying---something DD does a lot too--
is it just Harry? Or does Snape make it a point to mislead with the 
truth? That might make it easier to foil the Dark Lord.