What about Dumbledore though? Ok, so Grindelwald probably wasn’t the master of it but surely Dumbledore won it by force, yet Draco took it away from him...
Well, yeah, but that's part of the legend that grew up around the wand, that it was "unbeatable". It wasn't really, no more than Harry's Invisibility Cloak could really hide him from Death. The wand (when it acknowledged its user as its true Master) just conferred a *lot* more power onto the user than did the average wand. But the user could still be distracted, caught by surprise, etc., as Dumbledore was. He was surprised by Draco, and had a split-second choice to defend himself or to protect Harry by keeping him out of the fight. He chose Harry, and so was "beaten" by Draco. Not the wand's fault, and I suspect that the wand "chose" to acknowledge Draco as it's true Master because Dumbledore didn't use the wand as the wand would have expected (i.e., to battle an enemy).
In the end, it still boiled down to the wizard, not the wand. :P
What about Dumbledore though? Ok, so Grindelwald probably wasnt the master of it but surely Dumbledore won it by force, yet Draco took it away from him...Dumbledore and the wand were occupied putting a full body bind on Harry when Malfoy attacked. In effect, D surrendered to Malfoy, since he could have defended himself, but decided not to. He wanted to be sure that he wasn't the last "master" of that wand before his death.
Mark