I'd argue the fact YC is an American incubator also has a lot to do with who YC companies target. A lot of internet VC-backed startups don't particularly depend on their users spending money.
My point was (fairly obviously) an analogy. However, almost all startups have one of two business models: either they sell things to their customers, or they sell advertising space to people who want to sell things to their customers. Both require customers who spend money.
Remember, if you're selling ad space, the advertiser is the customer. The user is the product. Nitpicky, but important. Your explanation works if you replace "customers" with "users".
