Broad answer: they "evaluate the fanbase and see if there's a market for it". More specific answer: "Sometimes we see games on eBay, and that's how you see what games people are willing to spend $80 on". That's Capcom's John Diamonon. Course, he's quick to stress that's not the only way they check, and it's probably not even near the top three mthods they employ. But it sure is an interesting one. Probably more effective than the blood-stained letters I've been sending them for the last ten years, threatening/pleading for a new Captain Commando game.