Original VC content may be why there are (what some people complain are) very few VC releases each week, and not too many good ones yet overall.
Perhaps they plan to stretch out the classic game releases over a span of like ten years (which is half the age of some of the games, I know...as well as carry on to the end of the console AFTER the Wii) so until they get some original VC content, they have to stretch them out to maintain interest. Or something. If you're a European who waited ten years for Super Mario RPG hopefully you won't have to wait another ten more.
I'm not saying that with VC content that we can bet on every good game that exists for an older platform to come out in a year or two for the Wii's VC, but it might make them more comfortable with releasing more of the good ones and earlier.
Logically, the good ones should be early if they are guaranteed to be constant downloads. People are bound to lose interest waiting, swear off the VC altogether, and boot up an emulator on their computer instead. I suppose that's another argument for original and new VC content.