I read that. It was interesting. However it's definitely the exception rather than the rule.
Things like Truecrypt are fine and "secure" in isolation, but it's very difficult to clear up all the crap that the operating system leaves behind. Windows is especially bad, but nothing I've seen is immune from it. Typically there's enough evidence left in unencrypted temporary files, or in unallocated space that the content of the encrypted volume doesn't really need to be considered. Of course there are exceptions, but I've never been so troubled by encryption that the job has to be abandoned. Even if an IIoC suspect has fully encrypted a drive (Truecrypt WDE, say) there's usually a few CD/DVDs of images lying around for easy access.
As with most aspects of computer security, people are the weak link.