Defending the BB HU

In reading HoH, he mentions that even a terrible hand, like 23o has a roughly a 30% shot against a non-pair hand. HoH is NL tourney, but the concept got me to thinking.

If you assume you play at least as well post flop as the person raising your BB, why is it wrong to defend with any 2? You're getting 3:1, maybe 3.5:1 on your money (3.5:1 if the button raises and the SB folds. A 30% equity easily would indicate a call.

You've got odds to call any non-overpair. Given someone has a pair fairly rarely relative to non-pair hands, and if we know we're a better post flop player, why aren't we defending any 2 from the BB?

However, ToP has us only defending something like the top 40% heads up. Is it just a matter of the bad hands are too difficult to play post flop? If you could see your opponents cards would defending any 2 be a no brainer?

I'm not looking to defend with 23o [img]/images/graemlins/smile.gif[/img], but I am puzzled why we don't defend more than we do. Defending with ToP's 40% of the time vs a theoretical 100% of the time is a big gap. What makes that 60% unplayable? Even if we defend 60% of the time, what makes the other 40% unplayable?