None of the companies you have mentioned have reached any sort of critical mass. Clones in those environments probably have some sort of edge that allows them

None of the companies you have mentioned have reached any sort of critical mass. Clones in those environments probably have some sort of edge that allows them to gain traction in market segments the biggest companies can't touch. Take Groupon. For relatively low-margin services, the vig is too high to use it (an OPEN forum discussion suggested that in some circumstances you may end up receiving 10% of retail, so you should either have 90+% margin or hope that yo get repeat customers), and that leaves an opening for companies with a smaller vig (e.g. LivingSocial)