Try considering the example I mentioned elsewere: MeeGo becomes an Atom-based success and HTC introduces an ARM based device. How will OVI work in that case? Will there be any application available for the HTC phone at the begginning?
For ovi to support multiple platforms:The vendors must provide multiple binaries, which is only possible for phones that are already released, or It must become a repository where the developers will upload source code (practically impossible for non-opensource apps).