In 2004 a very draconian tax law was passed that has hosed expats royally. The bits that got all the attention were the reduction in income subject to tax credits, but one other nasty aspect is the requirement that expats NOT be present in the US for more than 30 days in any given year for the next ten years after they expatriate, else they fall back under US taxes, even for things like inheritence tax.
That is probably what that person is referring to, and yes, the laws have been changed in ways that are very unfavorable, and very unfair, to anyone wishing to emigrate. When discussing this with my co-workers, I have likened it to a "fiancial Berlin wall" which, whether or not it was deliberately designed that way, has the effect of financially trapping most people in the US, unless an employer is sending them abroad. In short, we're free to move about the world at the behest (and expense) of our corporate masters, but any individual wishing to do so on their own better watch their step (and move out in January)! I'm still trying to find a good US/UK tax advisor, as this is all about to bite me and my wife when we expatriate next week (and we don't even know if we're going for 1 or 2 years, or longer).
That tax thing is a nightmare, regardless.