would this accessory work with previous games that came out before it??
No. It requires specific programming for the new hardware.
Question.
Is it because of the Wii's lack of a hard drive/ memory solution?
I say this because many games on the HD consoles get patches regularly. Couldn't WM+ functionality be patched into some games? I don't think it would be practical to do so because it would probably require a few months just to get it working on one game, which is pointless as you can use those people to make a new game, but I'm just curious.
Anyway, if any company can get people to buy additional add-ons, it's Nintendo. They did it in the N64 era, I'm quite sure they can do it now. And maybe if you make a game that uses it (Monster Hunter 3 seems like it would be an amazing use of it), you can cut a deal with Nintendo to get it included with your game.
Didn't Capcom get a deal like that with REUC or something? The light gun periphrial? Or was that another light gun shooter? I'm not sure, but if Nintendo would include something like that in another company's game, I don't see why they couldn't add WM+ to big, more epic games games that use it.
Anyway, if you guys need any ideas on how to use it, let me know, I have a few. Though I'm sure you all do as well, after all, this gives the Wii much much more potential. :D