I think this is individual personality as Athena never barks unless commanded and it still like she doesn't know how or doesn't enjoy it, but she will whine. Apollo on the other hand will bark at anything, pants, shoes, cats, you name it. I have however noticed from being around some other boxers other than my own that they are typically non vocal, then again there's is my personal experience. Others may have different opinoins.
My boxer also seem to completely ignore other dogs barking across the block even when there's like 10 of them barking, it doesn't seem to bother them, it seldom even gets their attention, if it does it last about 20 sec. then they're back to rummaging around.