Virtual Domain

[Me]

If a server software can handle one domain, why can't it handle two or 
more in the same manner?  Why must other domains be seen as somehow less 
in importance by labeling them "Virtual"?  Regardless of where the 
server is physically located IP-wise, why not just design the software 
to do multiples of its basic function?

I hope the reader can see the relationship between these questions.  
Feel free to ask for clarification on any point.

Thank you.