The data I've seen shows the income where happiness flattens is around 100k rather than 70k so cutting off at 128k doesn't seem high enough to disprove the established research.
And that's why the cap for Nigeria is at $8k...
In fact, as someone else has commented: https://news.ycombinator.com/item?id=7047548
"According to the paper (page 13), they only look at incomes between the 10th and 90th percentiles. That's why they cut off at $128,000 for US residents"
In my opinion, ignoring data from the top 10% earners is the perfect way to get plots that seem to disprove a paradox that states "Become rich enough, and a bigger paycheque no longer leads to more happiness".