I made another topic about this, without even seeing this one! o_0
One thing I didn't see mentioned here was that with third-party games, and Sega games, and third-party games for Sega consoles, and whatever else they could scrounge up that would be worth the trouble (other region games?), Nintendo would have a monopoly on the past. A good-sized chunk of gaming history in a little package.
And while some people would see that as a knock against Nintendo, appearing to be "living in the past", any older gamer who's been gaming most of their lives will have to have some nostalgia for something if the Revolution can emulate Sega games as well as Nintendo games. If older people are buying the Revolution for the classics, they might pay attention to new games that come out for it. Most of the people that I've talked to that don't support the 'Cube simply aren't aware of the games for it. But if they had one, they would look and listen for Nintendo games instead of tuning it out.
Penetration into the older market this way via the classics might be a certain strategy. A 25-year-old might not be too excited about a game like Super Mario Sunshine, but they might be longing for that old copy of Super Mario Bros. 3. Or, as in the case of discussion, some Sonic The Hedgehog 2.
Monopoly of old games = good for Nintendo.
Older market's interest piqued = good for Nintendo.
Old Sega games possibly selling better than Nintendo's? = inconsequential, IMO. Getting that monopoly is worth any amount of retro-pride. Besides, I doubt it would happen.
The question is if it's worth surmounting the legal and technical issues surrounding it, and I know it's easy for me to say, but I'd say so. Many Nintendo gamers have played the best Nintendo games, multiple times, even. Playing a few Sega games and paying Nintendo a bit for the privilege of doing so can't hurt Nintendo one bit.
Nintendo still hasn't fully shown its hand. We don't know the true revolutionary nature of the Revolution, whether it's just in the controller or something else altogether, but we can see from this game download service alone that they have at least one ace up their sleeve. They just have to play it with the right combination.