I think Microsoft did a good job with its drivers program. It was solving different (but similar) goals, and the bar was kind of high, but they essentially did a good job with their driver signing system. A web of trust approach is not horrible. You should know the reputation of software publisher before you install an app. App stores do a lot of static analysis and screening, and they yank unsavory apps, but their profit motive is suspect and inevitably biases them towards maintaining that model rather than giving the optimal environment that favors users and publishers.