I'm sorry I couldn't reply before, but thanks for answering.

I've done more research and I found out that the contacts that are missing are all contacts that exist only in my Google Talk account: they don't have phone numbers, the only field they have is a GTalk login and their names are all under nickname, instead of first and last name. Running Hermes from the Terminal shows that it counts to a certain number, exactly the difference between the total contacts that I have and the number of contacts in this situation.