Many many times the actual ceremony is for close friends and family, and the reception for those who are not as close to the family as those who attend the ceremony, or for those who are acquantances but not "friends" etc. For my sister's wedding, the ceremony was held 4 hours before the reception and invites were included in the entire wedding announcement for those who were invited to the ceremony itself. Often too, if it a smaller venue, there may not be room to invite everyone, and receptions are often held at large places to accomodate the extra people. The ceremony itself is quite private and family oreinted where the reception is more party oreinted. It's not uncommon at all. There were over 300 people at her reception, but not everyone was so close that they were invited to the ceremony, many just casual coworkers etc.