Singapore is one of dwindling number of countries that rejects the idea of dual citizenship, so it could be that they just wanted to become Singaporean citizens, in which case they have no choice but to renounce their US citizenship as a condition of doing so.
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Eduardo Saverin (of Facebook fame) is also on that list. Also in Singapore, I think. I wonder -- what their reasons are other than the US tax burden?
A cursory glance at Wikipedia suggests his middle initial is P. The middle name listed on the register is Luis.
http://en.wikipedia.org/wiki/Eduardo_Saverin
A cursory glance at Wikipedia also suggests that "Since 2010, Saverin has lived in Singapore."
Singapore is one of dwindling number of countries that rejects the idea of dual citizenship, so it could be that they just wanted to become Singaporean citizens, in which case they have no choice but to renounce their US citizenship as a condition of doing so.