It should be, but the IRS doesn't catch every cheat, and as with most other white collar crime, the responsibility can be laundered through a number of accountants and other professional staff, resulting in fines rather than jail time.
So a lot of rich people make a lot of questionable calls regarding how their assets are categorized and if they get caught out they generally just pay what they're supposed to have paid, or sometimes slightly less (some countries have legislation prohibition tax authorities from accepting settlement offer at under-assessed amounts, but there are ways around that too). If they're particularly risk-averse and ballsy, they'll ask for an advance ruling certificate or another pre-emptive ruling on their filings to confirm they're correct beforehand. You can bake those too, if needed.