I think that perfect pitch can be developed, and I agree with the person that said that there must be at least a capacity for it to develop. I've seen some people who aren't even close when identifying notes and others who come within a half-step. I believe that those who can naturally identify a note within a half-step are probably the ones who have the capacity but never recognized it.
I have perfect pitch. When I was younger, I did not know what it was. Although I learned to play the piano, arrange, compose, and take melodic dictation without a teacher, I did not know what was allowing me to do this. At the age of six, I would hear melodies and know what key it is in by finding the starting note on the piano. It was like something always drew my hands to the correct notes even though I did not know the names of all of the notes at this time. I was able to tell what key a song was in, but not by name. (For instance, a song in G major, in my head, would be "a song in the white key that has one black key at the end of the scale). :D
I was uncomfortable when hearing a piece transposed and in aural skills classes where they transpose the melody to make it easier on others. I never understood why I finished dictation tests before the others or why they did not know the notes. There are many "idiosyncrasies" associated with perfect pitch and things that I did not understand about the way that I heard music until I was told that I had perfect pitch. Since then, I feel better about being a musician because at first, I thought that I was "weird" or that something was wrong with me. :ermm:
During this time, I would sometimes confuse the semitones. However, ever since I've found out what perfect pitch is, I've found out how to use what I have and it has improve dramatically over the last two years and I've done nothing to make it improve except use it - which I wasn't doing much of at first, because I didn't know what it was. Now, I seldom make a mistake. :)
If perfect pitch can improve - maybe it can be learned as well.
Another tidbit: When I was a kid, I went to my friend's aural skills class in college to visit. At that time, the instructor gave a dictation test. After she played the melody once, I knew it already. I did not understand why they needed seven more playings of it in order to figure it out - and some of them still did not! I still did not think that I was any different from them or anyone else. :D