I wouldn't call the voice a "nit pick". I would say an actors voice is pretty significant.
No it's definitely nit picked.
It's not something that alters the quality of a movie. Which is what people pretend it does in extreme cases. Bale obviously approached the portrayl that the Batman persona is an extreme act put on by Bruce. The voice is kind of logical, and gives energy that brings the performance to life. Along with his leaning posture that indicates anger and ready to pounce. The Bale bat voice has been imitated countless times already. Haley's Rorschach, the new Dredd, etc.
Keaton, and Bale both saw the absurdity of putting on a Bat suit. And you can't put on a normal performance. Look at the test footage for BEGINS of the people besides Bale. It looks even goofier, and wordier if someone just talks normal in that suit. It instantly becomes more absurd, and un-intenionally hilarious.
Keaton played it internally, crazy, and with his eyes ... minimal dialogue. His posture was relaxed, with a cool swagger. Keaton's Batman was a true split personality. His second skin. He was Batman, Bruce was the shell.
Bale made it an act put on by the Bruce Wayne character he was portraying. If he wants people to believe he's a giant Bat monster, why wouldn't he speak like that in a gravely, gritty tone of voice? It's not human, it's seething, and demonic.
Besides a few scenes where it sounded goofy due to action, the way his mouth moved or the character being out of breathe "You'll be in a padded cell forever" ... and "You never would've gave it to an ordinary citizen" ... it sounds totally bad ass.
It's almost become iconic now with the character. And he was described as sounding like that in the source material a few times. So you can't even claim it isn't accurate. I applaud the balls Christian had to implement it into his performance, regardless of how polarizing it would be.