To me, the answer is real easy - I know Resident Evil. I like Resident Evil.
Now, I'm not a Wii-only owner, but I am mainly a Wii-gamer. I play my 360 from time to time, but I hardly pick up every big game that hits it. As such, I did not pick up Dead Space - Something many others also avoided doing, going by it's sales numbers. Also, Wii-only owners would not have bought it at all, because, well, they can't play it. Therefore, my incentive to buy a spinoff to a game that I've never played ... Is very low.
Regardless of it's high quality, it's still a spinoff of a practically non-existant franchise. It's like they're trying to get it sold on brandname recognition when the brandname isn't even established.
Resident Evil: The Darkside Chronicles is nostalgic for many (not for me, though, since I never played the RE-games way back when, my first was RE4 for Wii), and it contains characters that are incredibly popular. Leon S. Kennedy, Claire Redfield - These are pretty big characters in gaming. I have no idea what the name of the main character in Dead Space is... Does he even have a name?
Also, people can be assured that Darkside Chronicles is atleast as good as it's predecessor since, well, it has a predecessor. Plain and simple, people know Resident Evil. People like Resident Evil. If it weren't for me camping gaming-sites, I'd have no idea what the hell Dead Space was.
That's my take on it, anyway.
