Boyfriend won't talk about his past, yet he asks me questions about mine!?

My boyfriend won't talk about his past relationships. He either avoids the subject or ignores it. I am bothered by this because he feels free to ask me stuff about my exes and such and I tell him. I am an open book and have nothing to hide. However, I don't think it's fair if he's allowed to ask me anything, but then he won't divulge when I ask him things (i.e. I asked him if he still talks to any of his exes and he did not reply, when he asked me why I still have an ex on my Myspace page and I gave him an explanation). I have heard that when a guy doesn't want to talk about an ex or exes, he still has feelings for them or has something to hide. Should I be worried? How do I approach this?