> If the government were to start taxing people on the value of their assets you can be quite sure that within a year or so most rich people would have their assets in a form that makes it much harder to value them.

Switzerland, which tends to be viewed as a haven for the rich, has a wealth tax. It would appear to be a counterexample...

Note that it has other tax features which may make it appealing to the rich (no capital gains tax, e.g.).