I've heard that children's memories are much more detailed and vivid prior to learning to write. Once written communication begins, we tend to rely more on writing down information (vs. solely on memory) and those incredible memories fade some.

However, that being said, my DS (5.11) continues to have a remarkable memory (despite developed written communication)
-His passion is for sports and scores (major games/his favorite teams, bowl games of past, etc. (this goes for football, basketball, soccer, baseball). It blows my mind the scores from years ago that he will accurately recall.
It was actually his amazing memory that led us to have him tested. (and he ended up being on the gifted spectrum).