Since no one else is going to bite...
Weddings have been commonplace in Ultima Online, not to mention within just about every other multiplayer online world out there, since the concept of the MMORPG first emerged. It may sound rather strange to some, but this actually makes sense if you consider aspects of social psychology and interpersonal relationships. It is the hallmark of a game that is more focused on socializing and creative collaboration (Ultima Online) than the endless grind (World of Warcraft). A world, rather than a setting.
Yes, the primary reason is often roleplaying. It is not uncommon for roleplayed characters (or RPCs) to develop deep bonds with one another, whereas the player themselves do not share these feelings out-of-character. On the other hand, this is not always the case. I know several couples, including married ones, who play games like Ultima Online togeather, and one of the aspects of the intimate relationship talked about by psychologists is the "Social Bond" or the public declaration of your relationship to the world. That is the reason for weddings, rings, and all that fun stuff RL. Although they've done it RL with friends and family, some like to publically declare their relationship to the virtual world as well, to their virtual friends and companions.
Its a way of telling the world you've claimed one another, and become one.
Just some food for thought.