The short of it – there are still challenges at the end of the message chain. The three regional centers were effective in communicating warnings and data to countries, but getting the message to the people away from the major cities was still a struggle. Countries can be strategic in determining which areas may be more susceptible to tsunami effects, and focus their efforts on those areas. But the investment in infrastructure is still significant, and the maintenance of these networks represents a non-trivial amount. Much in the same way that the infrastructure in the U.S. made it easier to manage the Ebola cases diagnosed in that country compared to the areas hardest hit in Africa, the communications infrastructure in Hawaii and other more developed coastal areas make it easier for tsunami warnings to be heard.
What the people do with the message when (or if) they get it is a separate question. Rational action in the face of natural disaster seems less correlated with level of development, but I’d love to see any studies that address this.