Customer Development is probably best for Enterprise level applications where you can speak with the head of a 100-person team and get an answer for everyone else.
For consumer applications, however, you can ask 1000 inidviduals and get a "No" while your product could still be helpful to 4 million others. For example when I ask my friends to switch from Yahoo Mail to Gmail they usually answer "What does Gmail do that Yahoo doesn't?" or "This is fine for me".
EDIT: What if Twitter followed a customer development model? They probably would not have written a single line of code.
Just to be clear--with customer development, you don't ask customers for your vision. That's still the founders responsibility. So yes, I think @ev and @jack would have still written code. They would have then asked people (not laggards, but people they already think might be interested) if their MVP has legs.
Regarding your edit, I don't think that the Cust. Dev. proponents say that it's the only way to develop products, but on average it will help you succeed. It also seems like Twitter used some concepts that CD also suggests. With such a simple product, they probably stayed at the MVP stage for a long time.
For consumer applications, however, you can ask 1000 inidviduals and get a "No" while your product could still be helpful to 4 million others. For example when I ask my friends to switch from Yahoo Mail to Gmail they usually answer "What does Gmail do that Yahoo doesn't?" or "This is fine for me".
EDIT: What if Twitter followed a customer development model? They probably would not have written a single line of code.