It appears to me that part of the reason the Silicon-Valley-Tech-VC model involves explosive growth is because a large number of the businesses are chasing what really amount to fads, and the only chance they have of being successful is to take the entire market before the uers move on to the next big thing, so that after the initial "wow" wears off, anyone that remains stays on their platform/program/app/service/etc.
Obviously, that's not entirely a bad thing. It's made a lot of money for a lot of people, and there are people who genuinely thrive on the churn and burn involved.
It's not a model that I personally like, preferring instead a slow and steady growth based around a lasting quality product. It might not lead to billion-dollar businesses, but I think it leads to better businesses.