IANAL but I imagine having the site open to all countries is a legal nightmare.
It's not that it's impossible or insurmountable, just that it requires effort that a start up may not be willing or able to put in at release.
Exporting isn't as easy as selling in your native country. People are able to do it because someone went through the effort of studying the laws of the country being exported to and determined that it would be profitable to export to that country.
And yes i do "export" my services to few countries so i would say i have experience with it.