The point of keeping games in separate virtual drives is that specific tweaks (specific versions of Wine, natives libs,...) can be used per game. You can install one instance of Steam and install games in it, but then you'll have to manage the tweaks and the required components by yourself.
Thanks for the reply :-) I did figured out about the purpose of virtual drive, and I have no problem using them (less work for me :-)). I was just curious whether Steam will recognize virtual drives as different Pc's or not (so that I'll have to add a computer for each game). I guess I'll figure it out by trying it :-).