Consistency, they say, is a bugaboo of small minds. :-)
Little things like that just bother me, like a dripping faucet: Why do wizards have flush toilets, but not pencils, for example? Why do they have radios, but not televisions or telephones?
(I know, just shut up and clean something ...)
Well, they don’t need telephones or email because they can communicate using owl post, talking patronuses, or 2-way mirrors.
No telephones because they can talk via floo powder. No television? What good has having television done us?
Ah, but the books are so well plotted that we expect them to be perfect, like Harry, Ron and Hermione keep saying Harry's cloak is throughout DH, forgetting that Moody's Eye, when worn by Barty Crouch Jr. in GOF, could see Harry through the cloak. I at first considered that a continuity flaw, but finally decided that it was in character for Harry to forget the exceptions that disprove his various obsessions throughout the series. I don't recall him ever mentioning this to Hermione or Ron, who might be more inclined to remember the shortcoming, although I'll have to check that when rereading 1-VII. The other two of the Deathly Hallows were well proven not to be as perfect as the children's story claimed, neither is the Cloak.
However, I believe I did find a continuity flaw on p. 194 within Kreacher's tale:
He [LV] made Kreacher drink all the potion.... He dropped a locket into the empty basin.... He filled it with more potion.Who or what refilled the basin after Regulus drank it and Kreacher swapped lockets? And who or what refilled it again after Dumbledore drunk what seems to have been the same potion. The basin was full when LV checked by turning the potion clear to see no locket. You could argue that the basin automatically refills itself and she could and perhaps should have written that, but she didn't and LV really didn't need such a feature. LV filled it himself. He certainly didn't personally refill it the next two times; he'd have discovered the theft. Kreacher didn't say he refilled it, nor did Harry and Dumbledore refill it in HBP. Hopefully she'll explain in her forthcoming Encyclopedia.
Harry Potter can be not just the savior (lower case for the Zealots!) of the Wizarding world. He also can be the savior of Muggles. Today too many validate LV's opinion of Muggles. They claim they are enthroning us, but their throne would be his. Muggles worthy of Harry, Hermione and the Weasleys' good opinions need to quibble with the big throne types and convert them to work for a world in which no wizard, goblin, elf or Muggle sits on a throne over the rest. Harry's story has the power to convert many. If they won't convert, stop mollycoddling them. Give them the full Molly!
"Sometimes you've got to think about more than your own safety! Sometimes you've got to think about the greater good! This is war!" — Harry Potter, DH, p. 568.