Is this hot water heater pipe corrosion normal?

(1) Needs to be connected by a nipple, only brass available
http://img4.imagetitan.com/img.php?i..._image6071.jpg

(2) Will the new brass nipple corrode just like the old did?
http://img4.imagetitan.com/img.php?i..._image6072.jpg

(3) Hot water outlet nipple seems to be steel?
http://img4.imagetitan.com/img.php?i..._image6074.jpg

(4) New & old nipples are both brass so why corrode?
http://img4.imagetitan.com/img.php?i..._image6075.jpg

(5) Cold water inlet has less corrosion it seems but why?
http://img4.imagetitan.com/img.php?i..._image6076.jpg