The root assertion of your identity is always a notarized statement — you can reset your entire identity by visiting a notary with someone with ID who can vouch for your identity, even if all your identifying documents are stolen (as long as they were previously in the system). And, of course, you can spread your keys across multiple widgets, so that the thief only gets your (locked) credit card, and not your (locked) passport, driver's license, social security card, etc.
The thing is that the widget isn't a black box — its specifications are well-documented. Everything about the inside of your widget is generally known except the contents of and keys to its secure memory — the secure memory keys are internal to the widget and known to nobody, not even you, and the ROM holding them is designed to fry itself if the widget is tampered with. Of course a determined hacker will be able to crack your card. However, I should think that the fact that a hardware attack involveng actual dissassembly is required to even buy a sandwich with a stolen widget would be somewhat reassuring.
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The thing is that the widget isn't a black box — its specifications are well-documented. Everything about the inside of your widget is generally known except the contents of and keys to its secure memory — the secure memory keys are internal to the widget and known to nobody, not even you, and the ROM holding them is designed to fry itself if the widget is tampered with. Of course a determined hacker will be able to crack your card. However, I should think that the fact that a hardware attack involveng actual dissassembly is required to even buy a sandwich with a stolen widget would be somewhat reassuring.