Few barriers to entry, really?? Sorry, but this sounds a bit like an inexperienced developer saying "Hey, I could build most of Facebook's functionality in 2 weeks." Booking.com is THE largest spender of advertising on Google. They have giant teams that A/B test the living shite out of every pixel on their screens, and huge teams of data scientists squeezing out every last bit of optimization on their site. It's a huge barrier to entry. This answer from Quora's CEO explains it well: https://www.quora.com/What-are-some-important-internet-compa...