The point is that you don't have a separate password just for the disk encryption. It all works transparently.
How often do you reboot your laptop anyway? It takes a couple seconds to type in a well-rehearsed passphrase.
When I reboot mine it's actually three passwords that I need to put in: disk encryption, linux login, and firefox master key.
The downside is after all that, is you end up with an running Ubuntu system, and you realise you're running a shitty NIH Debian fork.