[Zope] Playing the Devil's Advocate: Why Zope?

Hi, My dad is finally considering rewriting his business applications from VB to the web... and asked me to check out the different tools available. I know a bit about environments like Zope, OpenCMS, am currently checking out VB.Net or "simple" languages like PHP. Could anyone experienced with those tools tell me why I should go for ASP.Net, or even what is the point of prefering more complex environments like Zope over PHP? Any hint much appreciated EvH.