Though part of me understands Kytim89's point (and Nintendo's, for not wanting to allow this to happen), even if 10% of people that try the demo follow through and purchase the full game, that's a huge incentive to offer these. I'm intrigued by all four of the chosen titles, but would probably only download the Bit.Trip one (having enjoyed the previous games). So if I try the ThruSpace demo, you're not losing a sale, since that wasn't ever going to happen. But you're gaining a potential sale, since if I love it I might just buy it. I know the reasoning behind demos are not some unknown science--this is more just me, thinking out-loud and trying to figure out why a company might think they're not a good idea in the first place.
Anyway. I'm excited. Weekly or monthly, I'll take it.