It annoys me too - I'd love to be able to play X-Boxes' SW:Knights Of The Old Republic or Halo and the old PC classics like Dark Forces or Tie Fighter on my GC too...
I really despise 'system only' games - all games all formats - it should be made into some sort of universal law! lol
If I find an 'all games - all systems' petition I'll be sure to sign it and let you know in them ean time if you could just sign the petition above...