Average Joes are not going to have to track all there btc spending. IRS has no way of tying you to a anonymous bitcoin address. Nor do they want to waste time on it. Pull your head out of your ass.
I think your right for right now. But this is a dangerous path to take. A few years from now the IRS may have resources that make it very easy to associate you with your bitcoins. They may audit you and if they discover in previous years that you have not paid gains then you will owe the principal + interest + fines. It is even possible that you are jailed for tax evasion. Such penalties could be far higher than your profits and you may end up loosing a lot money.
Anyone who wants to try tax evasion should be aware of this and understand the financial risk you are taking by hiding profits from the IRS.