Another interview... the people from guildwars2journal.com managed to get developer Mike Ferguson to answer a couple of questions about the World vs World pvp combat:

GW2Journal: How has WvW changed since first conception? For example did you have any ideas or features you were looking into that you had to throw out during development, if so why?

Mike: One big thing that stands out in my mind is the supply mechanic. Supply was originally slated to be two different resources (wood and stone) that would be used to build siege weapons and upgrade objectives. Only one type of resource was available from each resource camp but you needed both types to be able to build siege weapons or upgrade your locations.
After playing the game for a while with two resources, we realized that it was actually a very confusing and frustrating mechanic as players were never quite sure which resource camps were actually more important for their team to accomplish their goals and it would cause strife between players who wanted to pursue opposing goals. Converting to one resource type that is available at every camp removes that potential conflict as players can focus on just gathering and using supply from any resource camp because it is always useful for their team.

GW2Journal: You have previously mentioned in interviews and on the ArenaNet blog that the number of players participating for each world may be limited. What happens when that limit is reached - are players put in a queue, can additional instances open up, or what other mechanic is in place to balance player participation and server performance?

Mike: Each map has its own population cap so we can ensure the servers will be able to handle the load without causing massive lag or crashes. If a map is full you can choose to enter a queue for that map or select one of the other WvW maps to play in.
We do not open up new instances or overflow servers for full WvW maps as the way the game is structured is not compatible with those concepts. We also would not want to open up a new instance of maps meant for hundreds of people when we may only need slots for 3 or 4 people from a World that try to enter a particular map when it is full. We'd also have to find ways to consolidate people from those overflow maps and reconcile what happened in those maps when the 'real' maps have spaces that open up and we wanted to move people back to that version of the game, which is a rather significant and very complicated problem to overcome.
See here for the entire article.