Interesting, but it's been a growing trend. US is one of the few countries that taxes its citizens who move abroad. This leads many to give up their US passport/citizenship. You may also know that US citizens who open bank accounts here in UK have to declare, specifically that they are US citizens. It's basically a checkbox you clear (or not). That is then flagged back to some 'entity' in the US presumably...

One thing I did notice that was interesting. If you click the 'raw data' from the Federal Register and scroll down the list of those who have given up citizenship there is one 'Steven Ballmer' listed..I had to chuckle at that one...