This shouldn't be this complicated.
Duke claims there's some sort of user-controlled-quality-regulation system in the works. My guess, it'll be a rating system that drops low rated crap out of sight and keeps higher rated stuff relevant, possibly with some sort of abuse reporting functions as well. That's just speculation, though!
Back to the point. Reviews are restricted to things that GR has added to their database for one reason or another, so this shouldn't be any different. The only change necessary is the addition of a section for "DLC," or "retro-rereleases," or something cooler I haven't even thought of yet. That would keep the reviews applicable to currently available products on currently viable consoles (Wii Virtual Console, PSN, XBLA).
Doesn't that sound lovely?