Dark Knight batman doesn't say "I'M BATMAAAN!" Internet Batman says "I'M BATMAAAN!".
Grumpy 50-year-old Batman says "I'M THE GOD DAMN BATMAN!"
But seriously though, saying Dark Knight Batman constantly says "I'M BATMAAAN!" is like saying Dracula constantly says "Bleh!"
"I'M BATMAAN" is a myth likely started by HISHE, just like "Bleh!" is a myth likely started by the count from Sesame street.
And Arkham Batman talks in virtually the same gravelly voice. Hell, there's "I'M BATMAAAN!" mods out there, he probably says it millions of times more often than Christian Bale has ever stated he's batman in the meme-ly fashion ever has, and ever will.