I think the biggest difference is that you can't (I think, Im a VB guy, not ASP) is that you cant handle the events. For instance, if you want to show a progress bar or whatever during a backup you'd dim the backup object 'withevents', then do some display update in the event handler. I dont think VBS handles events, taking a quick look at the docs at http://www.msdn.microsoft.com/msdn I don't see withevents as a supported keyword.
I think there is a way using the Windows Scripting Host to capture the events, but it struck me as a hack hardly worth taking (someone prove me wrong!).
I would also think that since DMO is built on COM, any language that uses or understands COM would be able to use it.
I tend to code my scripts in the VB IDE, then do a quick "conversion" to VBS if Im going to run as a job (though often I will just compile to a dll and run that, this is a good way to bypass the 4k limit on job text), I havent found any real problems with using VBS to accomplish what I need.