1. You could do the same thing with cash or gold in many domestic cases. Transferring a substantial amount of cash in/out of a BTC exchange is going to require AML paperwork and the blockchain/exchange has enough information for a regulator to back out where the money went. You might be able to trade locally for cash to avoid this, but for serious amounts of money that could get you robbed or arrested.

2. BTC can be devalued by the actions (or inaction) of other participants in the market and their value changes wildly compared to major currencies. Yes there will never be hyperinflation in BTC terms, but your BTC could easily end up worthless in other ways. Furthermore, I don't think this is a real risk for actual wealthy people. Their wealth is primarily concentrated in ownership interest in businesses, equipment, land, etc., not in currency.