I think the law of laziness applies here just like anything else. If bad guys really want your stuff they will get it. Nothing has changed there. The good news is that 9 times out of 10 if your laptop is harder than the next guy's to hack, then they will leave your stuff alone and get the next guys. Is this attack really plausible?

The big problem I have with this hack though is the lack of time you have to do it. If someone locks their computer and walks away, then you have a lot of time to do it. You can snatch the laptop, take it home and perform the hack (Hopefully they have plenty of juice in their battery). If someone powers down their laptop before they walk away, now you have to race the clock.