The Samoan companies that do business mainly with the USA are in a minority. They're also a heavily religious and family-oriented culture and aren't about to start working on Sunday. It sounds like you might be confusing Samoa with a more business-oriented culture.

So they just change the definition of when Sunday is to accomodate?

Yes. To quote Jesus Christ (in translation, of course :) "The Sabbath was made for man, not man for the Sabbath." Or to put it another way, you're only hurting yourself.

To be specific, the Sabbath is the last day of the week, so all the Christians who use Sunday both as the first day of the week and as their day of rest are already ignoring the Sabbath.

If you're interested in how that happened, it's to celebrate the resurrection of Christ, which was on the day after the Sabbath (because Jesus was crucified the day before the Sabbath and rose on the third day, the day after the Sabbath). So no matter where you put the Sabbath, Christians will still observe their day of worship on the day after.

Easier to do it that way. Just like how it's easier to devalue a currency for a nation rather than give every single individual in the country a pay cut!