Where is it stated that there are no SEA servers?

There were blue posts long ago about SEA having their own servers. Now we are defaulted to the US servers. This doesn't mean that there's no SEA server anymore. And I believe that is what the OP is asking - for someone who knows whether there is a SEA server or not, not a bunch of comments from people who are reading between the blues lines.

Could we get a decisive answer from a blue: Is there a SEA server?

Sure,

Diablo III's global game servers are grouped into three distinct game regions:

The Americas - For players in the US, Canada, Latin America, Australia, New Zealand, and Southeast Asia.

Europe - For players in the European Union, Eastern Europe, Russia, Africa, and Middle Eastern countries such as Israel and the United Arab Emirates.

Asia - For players in South Korea and the regions of Taiwan, Hong Kong, and Macau.

Further details can be found in the blog post here.