Releasing old games on a download service akin to iTunes is much different than re-releasing a game for a current system. Games that you buy for GBA, whether they're new or old NES games, still have to cover some costs, namely manufacturing costs of the cartridge and such. With a downloading service, all they're paying for is emulating the games once, which costs almost no money and takes little effort, and then maintaining servers, which $1 a download would more than cover. Even at that price they'd still be making a very nice profit, especially if they raise the price to $5 or so for N64 games.
Let's say after a year or so of the Revolution releasing, they've sold one million NES/SNES/N64 game downloads on their virtual console service (they're probably do this after a few months, but it's theoretical anyway), with each game costing $1. That's one million dollars. I guarantee you it costs much, much less than one million dollars to emulate a selection of games and to maintain their servers for a year. Even at $1 a game I suspect it would be more profitable than releasing games, because you have to manufacture the cartridges and boxing, you have to ship the games out, nobody will be picking up used copies - really, it's just a better way to sell smaller-sized games overall.