The short sellers overlook the network effect, where the network becomes more valuable with increasing number of members. Perhaps Angie's List reached the number of members needed to make it a self sustaining growth company.
The video instructs the surgeons to check for staples protruding beyond the surface of the jaw after installing the cartridge, and if they are, then replace the cartridge with a new one. Invariably, by Murphy's law, the surgeons will become complacent, and fail to check for protruding staples. That might cause faulty staple deployments and maybe bleeding or leakage. The surgeon wouldn't know if it was because he forgot to check for protruding staples or because the stapler is inherently flawed. Word of mouth would be unkind.