You will have to forgive my ignorance but I guess my other concern would be is there even a way for GNOME to handle such verbs at the moment? I was looking at http://www.freedesktop.org/wiki/Specifications/mime-actions-spec and it seems like there is plans for this but, at least according to that page the spec for this is still in development. Also, just playing around with a few files on my desktop I could not find any useful way to invoke verbs other than open, but maybe I am missing something...
Another drawback of using a general "wine start" to call the windows apps is that we sacrifice a bit of desktop integration. It would be cool if the Linux mime type generated from the wine registry contained the application's name and icon, instead of some "Open with Wine" name.
I don't know if the registry can assign multiple programs to one mime type, but KDE can also offer a list of programs if multiple apps can handle one mime type. If a user has e.g. Internet Explorer and Win32 Opera installed, then he should see both IE and Opera next to the Linux apps he has installed, and should be able to select a default for KDE/Gnome, without having to select a Wine default too.