Last year, my best friend and I had the same exact dream the same exact night. It wasn't about symbolism or anything like that. In our dream, I was at home, cleaning, and she burst through our front door and was all excited, and told me she had "made a decision," and something to do with she was leaving the guy she had been seeing, because he was no good for her, and that she was having a baby without him.
I had told her my dream, but I was a little hazy on it, and couldn't remember some things word for word. She turned white, and she filled in everything, every word, what happened next, and it gave me chills, cause it jogged my memory, and what she said happened DID HAPPEN!!
I was skeptical when I'd heard about situations such as this, but when it happens to you, it's FREAKY and it's REAL. It angers me to read when people are calling other people liars. They think that just because it hasn't happened to them, it mustn't be true.
It DOES happen, cause it's happened to my friend and I TWO other times since. If you find out any info on this, please let me know, I'm curious as to why it happens, too.

Sometimes people with very strong connections find themselves thinking the same things at the same time, it is possible to dream similarly as well. I suspect there may have been a trigger (a conversation, a TV commercial you both watched, a news program, etc.) which encouraged the similarity.
As to why it happens, I don't think anyone can say. No one really knows why we dream what we dream.