I think that Betty Edwards and 'drawing on the right side of the brain' might have the answer here.
Briefly, she explains that people have difficulty drawing because instead of actually really looking and seeing what's before us, we just let our left-brains fill in what we think we see. So instead of actually seeing a chair we think 'it's a chair seen a million of those before' and then fill in details using our 'generic'
ideas of what a chair is.
So when it comes to eidetic memory we don't remember what we saw because when we try our left-brain fills in with the generic information. And probably, we never really properly looked at the thing in the first place!
What this means to memory development i'm not sure.
But Betty Edwards' book is wonderful and everyone should read it!
Have fun!
Nick 
