I wonder if the snapchat / facebook situation is more a suggestion that the MVP-then-launch approach to startups is more risky than some allow for. If you just release an MVP it may not have enough in there to be a solid finished defensible product, containing just your hook to test if you can get momentum. Then when BigCorp sees the hook, if you get enough success with the MVP they're heavily incentivized to take the next leap before you do, and they have more resources - you're still working at the underfunded MVP stage. Then you go from Lean Startup to No Startup in short order.

Just thinking out loud.