The IRS has simply given us their interpretation of how the existing laws apply to bitcoin.  The IRS has said nothing about the practicality of enforcing these laws.  These IRS statements give the taxpayer and the IRS auditor guidance.  If you follow these IRS guidelines you aren't likely to have any legal complications.  If you decide the IRS is wrong and you do get caught then I suppose you could probably bring the IRS to court but it'll be an expensive and uphill battle.

Personally I assumed BTC was subject to capital gains long before this.