[Wine] question about WINEPREFIX

[Phobos]

I wanted to ask to the wine experts something about WINEPREFIX or the crossover bottles...

how does the concept of "bottles" compares/differs with the concept of application virtualization (http://en.wikipedia.org/wiki/Application_Virtualization) used by VMware's Thinstall (http://www.thinstall.com/products/virtualization_suite.php) (aside for the .exe container*) and Microsoft's Softgrid/Application Virtualization (http://www.microsoft.com/systemcenter/softgrid/default.mspx)?

*I have used Thinstall a bit and it encapsulates all the files required by the app to work in an exe, including the registry keys (they call it "virtual registry") 

aside from these two products, how does it compares to the portableapps (http://portableapps.com/) process (which is in turn similar to thinstall but it's not an automated process and doesn't have the "virtual registry")?... why do the bottles need a "whole" c: drive?