Those retro titles often sell for a dollar - literally. Retro stores ramp up prices - they're not the only places you can get old games. There are always flea markets, EBay, garage sales etc., not to mention that many users still
have their retro games, so re-purchasing them makes no sense whatsoever.
As for Nintendo's built-in emulators, they reach great performance due to per-game patches but lack in every other aspect - homebrew emulators simply have more options to choose from, including Save States, Real-Time Saving, Screen Capture and whatnot. Built-in emulators give you what's essential to play the game and nothing beyond that, and that's
"too little" for some users.
Also, I'm not sure if it's not too late to post this... who am I kidding, it's never too late to post this...
Virtual Console, huh?