MSFT and AAPL both benefit from immense network effects, which translate into high LTVs (Windows/Office platform, iOS ecosystem). The presence of a strong network effect can often be a strong driver of virality, if not a prerequisite for viral acquisition for a lot of businesses because the incentive to share is directly correlated with the value delivered to the user/customer.
i'm inclined to believe that the probability of jobs resigning, especially after his medical leave in january, was already priced into the stock.
this would imply the market prices steve's value to the company > the 5% drop we saw after hours, since the 5% drop should reflect the incremental change of P(x) = 1. i'm not saying the stock won't take a huge hit tomorrow, but my bet is that it recovers in the near-to-medium term.
i am also not saying that the market is right - i wholeheartedly believe the company and its management can execute on steve's vision and has been for some time without daily guidance.