The 10% that succeed won't need that kind of scale on the day they launch though. Probably not even the first 12-24 months after they launch. There will be plenty of time to see what kinds of traffic they really can expect and then plan for that.
In other words; I can build them something for $10,000 that gets them to market in a month that may not be what they need in five years or I can build them something for $100,000 that gets them to market in a year, meanwhile, their scrappy competitor launched 11 months before them.
In other words; I can build them something for $10,000 that gets them to market in a month that may not be what they need in five years or I can build them something for $100,000 that gets them to market in a year, meanwhile, their scrappy competitor launched 11 months before them.