One of the most appealing things about vinyl is that it can bend certain structural limits when combined with other vinyl parts. Since there is a more generous amount of "give" within a connection, neat cheats abound. Things that would normally retain a very rigid formation in another material are suddenly granted the ability to move, even if just a little bit, allowing for more options in a base configuration. The end result is a more organic connectivity between components. The PVC has this to a certain degree, but the rules are tighter, and in general have to obey the fit function assigned to each part. With rotocast vinyl you can cut a matching diameter hole into a piece and develop something completely outside the prescribed options. I think this is probably the greatest draw for me when building or playing with vinyl in general.