How do so many startups register domain names similar to existing businesses?

This has to do with whether there is a 'likelihood of confusion' between your good or service and existing ones. For this reason the US Patent and Trademark Office allows for registering within certain 'Class'es of product or service. For example if someone started making books with pop up faces (somehow) they might well be able to call it Facebook. I cannot imagine where a .co or any of them would lose that likelihood of confusion although there are several different countries which allow for registration in that country. This also holds true for the European Community. I am licensed in the US, England and Wales with an LLM in International Intellectual Property if I may be of further service. Alexander@PenleyGlobalLaw.com