It seems to me that one benefit of operating under the 'chiptune' label is that it's a niche area with (as chunter points out) an existing organised network of people behind it. The average rock band faces the dilemma of figuring out exactly who to present their music to; there's a good chance it will get lost in amongst the other 1000 guitar-band-style releases that month, unless they're applying a very specific label to themselves that allows people to find them more easily. I guess the same applies to any broad description, 'electronica' or what have you.
Also I find myself downloading & enjoying chip releases that, genre-wise, might come under a category I would normally avoid. Same applies to chip gigs - you see shows with 5 artists all playing arguably a different genre of music, but chip fans stay and enthusiastically enjoy all of them. Being open minded is part of it, I guess, but the chip source is the unifying factor.
Totally agree with 4mat & Decktonic about a required purchase (in whatever form) legitimizing a release. It doesn't even need to be money - alternatives like giving an email address for an album download, tweet for a song, etc. still require a commitment from the listener and give something back to the artist. I think it's worthwhile to have some stuff available at no cost & with no strings attached though.
Anyway, download stats:
Challenge! - 626 since December 2009
Comptroller - 381 since March 2010