Are virtual worlds necessarily small ?

Virtual worlds are much smaller than real world. The largest one, Second Life, is a few thousands square kilometers. Real world is roughly million-fold larger than that.
In the case of WoW, we can argue it is because it's expensive in terms of man power to build such a 3D world. But in Second Life ? There are people willing to build wonderful 3D spaces. But they cannot, because the terrain is too expensive (compare to webpages or blogs that are free). They have to pay a monthly fee to Linden Lab. So the scarcity of content is not the real reason and with a free (like beer) terrain, virtual worlds would be larger.
Is Second Life making good money out of closing its doors to these potential contributors? Probably not. This problem have its roots in the technical architecture of Second Life. There is a server in charge of each 65536 square meters parcel of terrain and this is weird. Most islands and sims are empty (see previous post) and need no computing power while some are desperately crying for more power as people come in. This is a really bad situation, most Second Life servers (70-90% ? SL crew must know) are running empty, sipping electrical power just in case someone decides to have a look at this portion of the world. And very often, this visitor do not stay and leaves the place short after entering, see previous post.
So while most SL servers are sleeping, totally useless, users are asking for more computing power, either to have they own piece of land or to be able to enter a place hosting an interesting -and therefore popular- event.
For Twinverse virtual world architecture, we have reversed the equation: there is a computer (more precisely a portion of computer) in charge of each user. And this is pretty convenient since every user have a computer at her hand when accessing a virtual world. OK, maybe you do no like this way of presenting things and just want to call that a peer-to-peer system. But keep in mind that this computer in charge of the user can be her own computer or otherwise hosted in Twinverse server farms, that's not the point. The important point to keep in mind is : the land in Twinverse is costless. No matter how big the world is, the cost is per active user.
So the world can be as vast as needed... As vast as Google Maps or Google Earth, as vast as the real world.