Few webapp concepts can't be reimplemented in a short amount of time. Seems to me often the key is in user base and quality of execution (tech & non-tech) which stealth doesn't really help with.

Of course startup founders can think differently and may be right, I just think the support for this in the community is amusing in light of the "radical transparency" chic we're all into now - do YC startups have more important/valid secrets than the US government?