I must admit that It kind of stuck out to me as well. When I saw BB for the first time it did a little bit but with TDK I remember thnking to myself..."the voice is a bit much Bale.." However, now that I've seen it multiple times I kind of get it more. The voice is not just Bruce Wayne talking in a whispery voice but rather a complete disguise as well as the whole fear thing. It seems a little exagerated but I can see how it makes sense. I do respect them for not just doing the Keaton whisper and talking in his regular voice like BTAS would not make sense and be even sillier.