Some devices make this very difficult. Well, not very difficult - just more time consuming. I was trying to unlock a BIOS password on a Toshiba Satellite maybe 3 years ago, none of the default or "backdoor" passwords would work. However, you were able to reset it by using a jumper to complete a specific part of the circuit.. Not for the faint hearted, however if a thief steals the laptop, they'll have no problem opening it up in their own time.

I'm glad they've made this harder, as most thieves are deterred by the technical aspects of breaking in to wipe a computer.