I've come to the conclusion that 90% of 'stealth' startups do so entirely out of psychology. It's cooler to invest in stealth startup, and the mystery builds notoriety. I'm not sure it has much if anything to do with the actual business at hand.
Personally, I think about this differently; Startups who are outspoken about what they do early on are generally hoping to benefit from inbound interest.
From what I observed in YC, launching a TechCrunch article typically doesn't lead to a ton of inbound interest (at least for B2B companies this is true - if you're Uber/Vine/Tinder/Grouper, it's a different story).
For B2B companies, press helps get investor attention, can help with inbound hiring, and can potentially help get clients, if your press releases are well targeted enough (which most aren't).
From our perspective, staying quiet was the default. Now we're at the point where we're interested in reaching a slightly broader audience.
