There was a bit more to it than just that. He could have used block-level encryption relatively safely if he'd made a series or hierarchy of Truecrypt containers and mounted them only when needed, rather than putting everything on just the one block device.

More importantly, his physical security was lacking, as he hadn't properly considered the threat model. If he'd been working in a secured area (like a locked room) where open laptop snatching was infeasible, that would have given him enough warning to close the lid, and maybe pop the battery out. Albeit still vulnerable to a cold boot attack, if law enforcement have such capacity.