In answer to Bob Sutor's question “If we didn’t have web browsers as we do today and started today to do everything that you imagine [for a distributed 3D virtual world], what would you create to do all that?”
I would probably create something very much like Second Life and open source the server source code.
Anything anyone ever creates is based somehow on someone else's ideas (standing on the shoulders of giants and all that). If we didn't have the web but we had video games, I would start with an existing gaming engine. Then in the absence of a worldwide network of linked information resources, I would take the next best thing to existing technology, science fiction. I'd buy Snow Crash by Neal Stephenson and start writing network protocols and file formats!
I'd start by separating the storage of content, logic and presentation into different formats and come up with some kind of distributed TCP/IP streaming protocol with heavy compression.
I suspect that you're asking whether the web is really a suitable platform for all this, whether if we weren't stuck in the mind set of the existing world wide web we might come up with a better solution. Perhaps.
But if I was creating the web from scratch (but happened to benefit from the hindsight of all the great minds that came after me), I wouldn't use XML-like syntax for web pages, I would use something more efficient. I would try to make the DNS system more decentralised and URIs would be of the form http:uk.co.companyname.department/resource instead of http://department.companyname.co.uk/resource. I might make HTTP requests asynchronous, build comment spam protection and Denial of Service protection into the protocols of the web. However, I wouldn't necessarily attempt to make those changes now.
What's amazing about the web for me isn't that it's perfect technology that could not have been done better, it's that it's openness and adoption has made it almost ubiquitous in the world. Creating new protocols suited to new applications is definitely a good idea, but if the online 3D virtual world is to become as ubiquitous as the World Wide Web, we should learn from the lessons of how web technology was created and build on an already ubiquitous platform. Adoption of a well defined standard is more important than a perfect technology.
Another motivation behind making Stephenson's “Metaverse” a direct extension of the web is device independence. It's all very well creating a 3D virtual world which requires a large amount of processing to render, but what if I want to access the information on a small information appliance with little processing power? What if I live in a developing country and want to be able to access some information but only have a text based browser? What if I'm blind and can't see the virtual world and want to hear it instead? We need not carry over all the limitations of First Life into Second Life. I don't know about you, but I hate having to pay for physical objects and I love flying!