I just noticed it redirects from sleep.io is all. It seems like while .com's are great, having something like sleep. whatever is pretty awesome. I was just curious as to why you chose one redirect over the other.
We decided that while we wanted to capture the .io domain for completeness' sake, for the reasons listed above (SEO implications, not "correct" usage of TLD), sleepio.com made more sense as the default / redirect target.